It's being billed as one of the most consequential midterm elections in decades, with a wave of Democrats hoping to capitalize on widespread voter dissatisfaction to oust their GOP opponents and win control of Congress.
They have their work cut out for them.
Thirty-five senators and all 435 House members face the prospect of losing their jobs in November. But political analysts tracking the races say that only a relatively small number of races — fewer than 50 House seats and just a handful of Senate races — are truly competitive.
A look at past election cycles helps explain why. Since 1964, voters have sent their incumbent House representative back to Washington 93 percent of the time. Senators enjoy only slightly less job security — 82 percent.
Academics have speculated on the multiple reasons that congressional incumbents have enjoyed an advantage over the years. Incumbents have traditionally used their positions to win favor with voters by offering a variety of constituent services or by pointing to increased funding they've captured for the home state or district. More recently, some have argued that redistricting has created politically lopsided seats that strongly favor one party over another.
Moreover, as the cost of mounting a political campaign has risen, incumbency in Congress has created an important financial advantage in attracting the money needed to win.
Since 1990, the cost of a winning a House seat has roughly doubled, adjusted for inflation, to about $1.5 million. If you're looking to win a seat in the Senate, expect to raise more than $10 million.
This time, Democrats are hoping to win control of the House by picking up 23 seats from the GOP. Based on the amount of campaign cash both sides have raised so far, Republicans are in a better position to defend their majority in the House than the Democrats are in taking it away.
As of the end of the first quarter, 221 House Republican incumbents had raised a total of about $262 million, or nearly $1.2 million each. Democratic incumbents had raised just under $950,000 each.
And Democratic challengers had raised significantly less.
In the Senate, Democrats face an even tougher job trying to win control.
If the Senate's two independents continue to caucus with them, Democrats only need to pick up two seats to win a 51-49 majority. But of the 35 Senate seats up for grabs in November, Democrats are defending 26 of them from GOP challengers.
And five of the eight seats that are considered "toss-ups" by one or more of the political pundits rating the races are currently held by Democrats.
That may be why Democrats in those races have been busy fundraising. So far, they've collected nearly $289 million, or about $11.6 million each, according to data from the Center for Responsive Politics. That's far more than the roughly $6.1 million raised, on average, by GOP incumbents.
But Democratic challengers have also raised far less than the $10 million it has traditionally taken to win.
More than 100 Democrats have entered races for open seats or to challenge an incumbent in Senate races. As a group, they've raised about $105 million, or a little over $1 million each.
Based on past races, that's not even enough to win the average House seat.