Next year's battle for control of the Senate has started to take better shape as new financial data this week showed which vulnerable lawmakers are struggling to raise as much money as their competitors.
Republicans hold a 53-47 edge in the chamber now. With 23 GOP seats up for grabs, versus only a dozen Democratic seats, a strong showing for the minority party could flip control of the chamber and help to determine what the next president can accomplish.
With President Donald Trump's reelection bid at the top of the ticket, the fates of about 10 senators in the year's most important races will be tied to the presidential race. Even so, a cash advantage can go a long way in determining who wins a close contest.
The House impeachment inquiry into Trump has added a new dynamic to the Senate races, forcing Democrats in red states and Republicans in blue states to traverse an even more perilous political minefield.
Take a look at the races that will determine the battle for the Senate below.
(CNBC pulled the amount raised by candidates from total individual contributions listed on Federal Election Commission reports filed earlier this week, which does not include transfers from other candidate or party committees. Individual contributions are considered a better gauge of voter enthusiasm for a candidate.)
— Graphics by CNBC's Nate Rattner
Trying to garner votes in a state where Trump won in a landslide in 2016, Jones has perhaps a tougher path to reelection than any other senator. His most recent fundraising haul should help.
Jones raised about $1.6 million in the quarter, ending September with more than $5 million on hand. Despite the structural challenges he faces in red Alabama, the senator heads into the end of the year with a big cash edge over his potential competitors.
Rep. Bradley Byrne, R-Ala., took in about $250,000 in the third quarter, ending the period with about $2.5 million in the bank. Former college football coach Tommy Tuberville raised roughly $370,000, closing the quarter with nearly $1.5 million in the bank.
The opponent Jones defeated in a 2017 special election, former state Supreme Court Justice Roy Moore, raised only about $63,000 and finished with roughly $34,000 on hand.
One metric should boost Jones' hopes: his net approval rating rose in the third quarter, according to Morning Consult. During the period, 41% of Alabama voters approved of him, while 36% disapproved.
The Democratic senator won the 2017 race in part due to low turnout and accusations that Moore sexually abused teenagers decades ago (the ex-judge has denied the allegations). Winning in Alabama again could prove considerably more challenging with Trump at the top of the ticket in a state the president carried by nearly 30 percentage points last time around.
Though he has tried to appeal to conservative voters in the state, Jones has voted with his party on key Trump priorities such as Supreme Court Justice Brett Kavanaugh's confirmation.
In terms of total receipts, which include transfers from other entities such as party committees, as well as total individual contributions, Jones had $2 million, Byrne had $381,000, Tuberville had $373,000, and Moore had $63,000.
McSally is one of the more endangered Senate Republicans running in 2020, aiming to keep a seat she was appointed to late last year. She enters the fourth quarter at a cash deficit in an already difficult race.
The senator's campaign raised a healthy $2.7 million in the third quarter, ending it with about $5.7 million on hand. But her likely Democratic opponent, astronaut Mark Kelly, took in money at a torrid pace.
His campaign raised $5.3 million during the period. Kelly's money in the bank, more than $9.5 million, easily topped McSally's resources at the end of September.
McSally hopes to reverse her fortunes in Arizona, which has started to look more like a swing state. The former House member lost a Senate race only last year to Democratic Sen. Kyrsten Sinema. Republican Gov. Doug Ducey picked her for the seat vacated by GOP Sen. John McCain's death, and the 2020 contest is a special election to fill the remainder of McCain's term through 2022.
McSally had a positive net approval rating in the third quarter, though it dipped slightly in that period. In total, 39% of her state's voters said they approve of the job she is doing, while 37% responded that they disapproved.
Despite her vulnerability next year, the senator has voted with Trump's priorities on nearly every major initiative since she took office in January. She notably voted Thursday not to override the president's veto of a measure that would end the national emergency declaration he is using to divert military funding to his proposed border wall.
The administration wants to pull $30 million from an installation in Arizona for the barriers.
An OH Predictive Insights poll found Kelly leading McSally by 5 percentage points in August.
McSally had $3 million in total receipts while Kelly had $5.6 million.
Gardner faces a tough road to reelection in a blue-leaning state. The fundraising prowess of his best known rival could make his 2020 task even more difficult.
The first-term GOP senator raised about $1.5 million during the third quarter. He finished September with a healthy $6.7 million in the bank.
His top rival for the Senate seat, former Colorado Gov. John Hickenlooper, raised just under $2 million for the quarter and ended it with $1.7 million on hand. Still, he had a little more than a month — rather than three — to take in money, as he entered the race in late August after dropping out of the Democratic presidential primary.
Former Colorado House Speaker Andrew Romanoff, considered the more liberal Democrat vying to face Gardner, raised about $430,000 for the quarter and ended it with just under $725,000 in the bank.
Gardner, running in a state that has drifted blue in recent elections, has also faced heat from Democrats for opposing the resolution to end the national emergency declaration. He has put the blame on Democrats for the administration diverting military money, arguing they made it necessary by not reaching a border funding compromise with the president.
In the third quarter, Gardner had the approval of 36% of Colorado voters, while another 39% disapproved of the job he is doing, Morning Consult found.
Meanwhile, an Emerson Poll in August — before Hickenlooper entered the race — found the former governor beating Gardner by 13 percentage points.
Gardner had $2.5 million in total receipts, Hickenlooper had $2.1 million, and Romanoff had $504,000.
Democrats will attempt to flip two seats next year in the red-tinted Georgia, following Sen. Johnny Isakson's retirement. In the year's regularly scheduled election, challengers have already crowded into the primary to face Perdue.
He heads into the final three months with a cash edge over his potential rivals — though at least one of them has shown the ability to raise money in a hurry.
Perdue hauled in about $1.1 million during the third quarter. He had a healthy $6.3 million in the bank at the end of September.
Democrat Jon Ossoff, a documentary filmmaker who fell short in a 2017 Georgia special election that was the most expensive U.S. House race ever, raised more than $800,000 in the three weeks after he entered the Senate race in September.
Other leading Democrats lagged behind Ossoff in fundraising. Columbus, Ga. Mayor Teresa Tomlinson took in nearly $370,000. Sarah Riggs Amico, a candidate for lieutenant governor in Georgia in 2018, raised more than $290,000.
While Democrats hope to make Georgia competitive after a closer than expected gubernatorial race last year, voters in the state largely like Perdue. He had a net approval rating of 22 percentage points in the third quarter, according to Morning Consult.
It is unclear now who will emerge as the Republican nominee to run for the seat Isakson vacated.
In total receipts, Perdue had $1.9 million, Tomlinson $382,000, Ossoff $1.3 million, and Riggs Amico $761,000 ($50,000 of which was an offset to operating expenditures).
Ernst is among the Senate incumbents in key races who lost the fundraising battle to a challenger in the third quarter.
The first-term GOP lawmaker raised just more than $500,000 during the period. Democrat Theresa Greenfield, the Ernst rival backed by national Democrats, raked in nearly $870,000 during the quarter.
An Emerson poll released this week found Ernst beating Greenfield by 7 percentage points in a potential matchup. The same survey showed Greenfield leading the Democratic primary field over competitors Michael Franken and Eddie Mauro, though 74% of those surveyed were undecided.
In Iowa, 39% of voters approved of the job Ernst was doing in the third quarter, while 43% disapproved, Morning Consult found.
Ernst has recently focused her energy on pushing for approval of Trump's replacement for the North American Free Trade Agreement as Iowa's agricultural industry takes a hit from the prolonged trade war with China.
Ernst had $956,000 in total receipts, while Greenfield had $1.1 million.
Collins has represented the blue-leaning state since 1997, and is now considered one of the more centrist Senate Republicans. But Democrats have poured more money and energy than ever into unseating her after her vote last year to confirm Supreme Court Justice Brett Kavanaugh.
Collins' campaign raised about $1.6 million in the third quarter. Her top Democratic challenger, Maine House Speaker Sara Gideon, raked in just under $3 million during the same period.
The incumbent still had more cash in the bank at the end of September, $7.1 million versus $2.8 million for Gideon.
Early polling in the race has found a healthy lead for Collins. Even so, another trend beyond Gideon's fundraising success may make the race more competitive.
The senator's approval rating in Maine has steadily dropped over the last two years. In the third quarter, 43% of voters approved of the job she is doing, while 49% disapproved.
Collins has cast two of the most consequential votes of her career during the Trump era. First, she joined with Democrats in 2017 to vote down a GOP plan to repeal major parts of the Affordable Care Act by the thinnest of margins. Then came the vote to confirm Kavanaugh, which erased the goodwill she had built up with many Democrats.
Collins had $2.1 million in total receipts; Gideon had $3.2 million.
Peters will have to fight to keep his Senate seat in Michigan, one of 2020's key presidential swing states and an area that helped to deliver the presidency to Trump in 2016. He got a couple early warning signs this week.
First, filings showed he got outraised by his Republican challenger John James in the third quarter. Peters took in about $2 million, while James raised $3 million.
Then, a survey by Marketing Resource Group, a Republican polling firm, released Thursday found Peters leading his GOP challenger by only 3 percentage points. James, a businessman and veteran, lost to Democratic Sen. Debbie Stabenow by more than 6 percentage points last year.
Another survey showed Peters with a much wider margin, however. A Target Insyght survey of about 800 likely voters taken Sept. 24 to 26 for MIRS News gave the incumbent a 53%-37% edge.
Peters has one of the better approval ratings among senators running in next year's key races. In the third quarter, 36% of Michigan voters approved of the job he is doing, while 28% disapproved, according to Morning Consult.
Another 37% said they did not know what to think of him — more than any other senator.
Peters had $2.5 million in total receipts, and James had $3.1 million.
Shaheen runs for reelection in a state Trump nearly won in 2016. Though New Hampshire could prove competitive, early signs show the second-term senator in a strong position ahead of 2020.
The Democratic incumbent raked in about $1.9 million during the third quarter. Shaheen's campaign ended September with about $4.3 million in the bank.
Her potential GOP challengers lag far behind in the money race. Retired Brig. Gen. Don Bolduc took in about $240,000 in the same period, ending with just under $150,000 on hand. Former New Hampshire House Speaker Bill O'Brien raised less than $40,000.
Shaheen, a former governor, appears well liked in the state ahead of her Senate reelection bid. She had a 20 percentage point net approval rating in the third quarter, Morning Consult found.
In terms of total receipts, Shaheen had $2.3 million, while Bolduc had $240,000 and O'Brien had $81,000.
Tillis could face a difficult race to keep his seat in a red-leaning state where Democrats have nonetheless enjoyed recent success in statewide races. Early indications suggest his top challenger is capable of keeping up with him in the money race.
The Republican incumbent raised about $730,000 in the third quarter. Former state Sen. Cal Cunningham edged Tillis out, taking in about $766,000 during the period.
Still, Tillis had an advantage in cash on hand at the end of September: he had nearly $5 million in the bank, versus $1.1 million for Cunningham.
The senator, who faces a Republican challenger in businessman Garland Tucker, has tied himself closely to Trump ahead of the election. Tucker has resources to deploy as he takes on Tillis: he raised more than $250,000 during the third quarter — and loaned another $425,000 of his own money to his campaign.
A third of North Carolina voters approved of Tillis during the third quarter, versus 38% who disapproved of the senator, according to Morning Consult.
The North Carolina senator has also faced heat for backing Trump on the emergency declaration at the border, particularly after he wrote a Washington Post column in February saying he would vote against Trump's move.
Tillis had $1.2 million, Tucker had $691,000, and Cunningham: had $1 million.
Democrats have their eye on pulling off upsets across Texas in 2020. Cornyn has the cash to make unseating him a huge undertaking.
The Republican incumbent, who first won election in 2002, took in about $1.8 million in the third quarter. His campaign boasted $10.8 million on hand to close September.
The top fundraiser among Democrats running for Senate in Texas, Air Force veteran MJ Hegar, raised just under $950,000 in the same time. She ended the quarter with roughly $900,000 in the bank.
Cornyn has stayed largely popular in Texas, even as Trump's popularity in the state has fallen. The senator had a net approval rating of 18 percentage points in the third quarter, Morning Consult found.
That's significantly better than Trump, who only had a 2 percentage point net approval rate during the same period.
Meanwhile, a Quinnipiac University poll in September found 23% of registered voters would definitely vote for Cornyn. Another 30% responded that they would consider voting for him, while 35% said they would definitely not vote for the senator.
Cornyn had $3.2 million in total receipts, while Hegar had $1 million.
Update: This story was updated to include total third quarter receipts for the Senate campaigns, along with total individual contributions, the original figure cited in this story.