FBI Director James Comey's October bombshell is already reverberating further down the ballot.
The surprise disclosure Friday that his agency is probing emails related to Democratic candidate Hillary Clinton has delivered a major blow to both her campaign and her party's hopes of retaking control of the Senate.
It's also created a headwind for down-ballot Democrats hoping to capture seats from the GOP in close races by winning over the remaining undecided vote. Many of the Republicans in those tight Senate races had sought to distance themselves from setbacks in GOP nominee Donald Trump's campaign. Now, the Comey disclosure has put Senate Democrats on the defensive.
The stakes, like much of the rest of this election, are high.
If Clinton wins, Democratic control of the Senate would ease confirmation of her appointments, including a new Supreme Court justice. A Republican-controlled Congress could effectively thwart much of any Clinton presidential agenda.
If Donald Trump is the winner, a Democratic-controlled Senate could provide a check on his legislative agenda, which would prove harder to block if the GOP controls both chambers.
While a number of House races remain close, the Democrats have a much slimmer chance of capturing the 218 seats needed to wrest control from Republicans.
To take control to the Senate, Democrats need a net gain of four seats, for a total of 50, if Clinton wins. (With 50 seats, her running mate, Tim Kaine could cast a tie-breaking vote.) If GOP rival Trump becomes president, the Democrats need a net gain of five seats, giving them a 51-49 majority.
So here's the math. Of the 34 Senate seats up for re-election this year, 10 are currently held by Democrats and 24 held by Republicans. Of those, nine are considered safely or likely to remain in Democrats hands and 17 are expected to remain in GOP control.
That leaves the eight toss-up states, seven of which are currently represented by Republicans: Illinois, Indiana, Missouri, New Hampshire, North Carolina, Pennsylvania and Wisconsin. In Nevada, Democrat Harry Reid is retiring, Republicans have a shot at picking up another seat.