President Trump and Republicans are fighting to maintain their coveted trifecta—control of the House, Senate and presidency, while Democrats are vying to gain a majority in both chambers of Congress.

Democrats are strongly favored to win a majority in the House, but Republican leaders insist they will maintain their control. The picture is hazier in the Senate, where the majority will be decided by several high-profile races in states such as Texas, Michigan and Alaska. To keep a majority, the GOP will need to win open seats while fending off attacks against vulnerable incumbents. Here are the elections and numbers to watch on Tuesday: If there is a single early barometer of the House races, it might be Kentucky’s 6th District, located around Lexington.

Republicans have held the seat in Bluegrass Country since 2013, but their nominee, Ralph Alvarado, is trying to hold off Zach Dembo, a Democratic former federal prosecutor. In 2024, Trump won in the district by 15 points, so if Dembo wins, it could indicate the Democrats are on track to flip enough red seats to win the House.

An Indiana congressional race involving Victoria Spartz, a Republican facing a tougher-than-expected Democratic challenger, could also be instructive. Those polls close at 6 p.m. local time.

At 7 p.m., most polls will close in Virginia and several will in Florida. Both states have a number of closely watched House districts. In Virginia, the 1st and 2nd districts are currently held by Republicans, but both incumbents are vulnerable. And in Florida, the 9th, 14th, 22nd and 25th districts were redrawn to favor Republicans, but Democrats are competitive in all four races.

Losses in all of these seats would eliminate most GOP paths to maintaining a House majority.

Every four years, political junkies watch presidential contenders compete for support in the Iowa caucuses. This year, the state could serve as a bellwether for the entire midterm election.

Republicans have held the governor’s office since 2011, but Rob Sand, a Democrat, is the favorite in that race. In the Senate contest, Republican Rep. Ashley Hinson, a former news anchor, is trying to keep a GOP-held seat against Josh Turek, a state lawmaker and former paralympic basketball player. Across the state, three of Iowa’s four congressional districts are considered up-for-grabs, according to Cook Political Report ratings, and could help determine control of Congress.

More than a decade ago, Iowa was a presidential battleground state, and many voters who once voted for former President Barack Obama swung to support Trump for three elections straight. Tuesday’s outcome could be a sign of whether that pendulum is beginning to swing back.

The number of voters casting ballots before Election Day can be an important sign of voter participation. As of early Monday evening, more than 57 million Americans have submitted early votes, beating the 2022 midterm’s final count by 25%, according to figures from the University of Florida’s Election Lab.

In Iowa, registered Democrats hold a strong margin over registered Republicans in early votes as of Monday, according to UF’s data. And in Maine, where incumbent GOP Sen. Susan Collins is fighting to hold her seat, registered Democrats outnumber Republicans by around double in early votes.

In Kansas, Republicans fear that price-pinched GOP voters will sit out of a close Senate race. But as of Monday, registered Republican voters have submitted slightly more ballots than registered Democrats.

Early voting is an imperfect measure. Not all states report party registration, and voters may vote against their registered party’s candidate.

The Last Frontier’s Senate race has been thrown a curveball with two candidates sharing the same name. Incumbent Sen. Dan S. Sullivan, a Republican, is being challenged not only by Democrat Mary Peltola but also by a fishing-village retiree named Dan J. Sullivan. The GOP argues that the latter could pull away unwitting voters from the incumbent Republican.

So far, Republicans have failed to get Dan J. Sullivan, the retiree, off the ballot. Both Alaska and the Justice Department have opened investigations into whether anyone broke the law getting the second Sullivan onto the ballot. The New York Times reported in late October that there was an organized Democratic effort to recruit him.

Federal laws don’t bar ballot stacking, experts say, but Republicans might push to deny Peltola the seat if she wins.

A celebrated tradition in American politics is the “October surprise”— late-in-the-race news that can flip an election in unexpected ways. But this year, two high-profile surprises against Democrats seem to not matter all that much and might even end up helping them.

Vivek Ramaswamy, the GOP candidate for governor in Ohio, dropped a surprise ad against Democratic opponent Amy Acton late in October. It featured Acton’s estranged mother urging Ohioans to vote against her, calling her a liar.

But the ad might have backfired. Acton’s mother has been separated from her since childhood, and she stayed with Acton’s stepfather after an Ohio grand jury indicted him over allegedly abusing Acton. Democrats and even many Republicans condemned the ad as inappropriate, and it was eventually taken down by Ramaswamy’s campaign.

And in Michigan’s hotly contested Senate race between Republican Mike Rogers and Democrat Abdul El-Sayed, another surprise—actually a November surprise—might not work for Republicans. El-Sayed’s Democratic primary opponent Haley Stevens pulled her support for him and instead endorsed Rogers at an event Sunday.

Democrats rallied around El-Sayed, issuing full-throated support for him and condemnations of Stevens. El-Sayed’s campaign had its best fundraising day ever after the news broke, raising $2.4 million on Sunday—including donations from over 29,000 first-time givers.