The close and uncertain battle for the White House has taken center stage this year. But Congress will play a major role in implementing (or blocking) the next president’s agenda — and the fight for the legislative branch is coming down to the wire.

Both parties only need to net a handful of seats to flip each chamber, with Republicans currently controlling the House and Democrats controlling the Senate with slim majorities.

Senate Republicans need a net gain of two seats to win the majority outright or just one seat if former President Donald Trump also wins the White House, since the vice president casts tie-breaking votes in the Senate.

In the House, Democrats need to net just four seats to take control of the chamber, and it is possible they could win the House even if Vice President Kamala Harris loses the White House. Control of the House could also be unclear for days, with several battleground seats in slow-counting California.

As the battle for Congress comes to a close, here are five things to watch:

1. Will there be ticket-splitters?

Both parties will be relying on the dwindling group of voters who split their tickets between the presidential race and down-ballot contests.

In the Senate, two Democrats are running for re-election in states Trump is expected to carry: Montana’s Jon Tester and Ohio’s Sherrod Brown. Both have relied on ticket-splitters in the past, leveraging their own personal brands and appeals to working-class voters.

But Republicans are betting that both states have shifted too far to the right for Tester and Brown to defeat their respective Republican opponents, former Navy SEAL Tim Sheehy and businessman Bernie Moreno.

(West Virginia Gov. Jim Justice is expected to pick up a Senate seat for Republicans easily in his state, where Democratic-turned-independent Sen. Joe Manchin decided not to run for re-election.)

Ticket-splitters could also play an outsize role in the battle for the House, where a slew of competitive districts are in states that are not presidential battlegrounds, like New York and California. There are 16 Republicans running for re-election in districts President Joe Biden won in 2020. While there are some signs Trump may be outperforming his 2020 margins in these districts, particularly in blue states like New York, Republicans will likely have to hang on to some Harris districts to hold the House majority. Five Democratic incumbents are also running in districts Trump carried in 2020, making them top GOP targets this year.

2. What impact could the presidential race have down-ballot?

The race for the White House is expected to have a significant impact on down-ballot races, especially in perennial battlegrounds.

Democrats are defending five Senate seats in presidential battlegrounds, including two open-seat races in Arizona and Michigan. Pennsylvania’s Bob Casey, Wisconsin’s Tammy Baldwin and Nevada’s Jacky Rosen are also running for re-election.

Their fates could be closely tied to the presidential race. In 2020, just one senator, Maine Republican Susan Collins, won re-election as her state voted for the opposite party for president. In 2016, every state supported the same party for president and for Senate. And this year, Harris and Biden have been key themes in congressional Republicans’ closing-argument ads. (More on that below.)

Some candidates, like Casey and Republican Dave McCormick in Pennsylvania, have been trying to strike a balance with the top of their respective tickets by appearing with their parties’ presidential nominees on the campaign trail while also highlighting areas of disagreement.

Several of these Senate candidates, like Rosen in Nevada, have been able to run ahead of Harris, as their GOP opponents have struggled to gain traction. But Senate contests in these battlegrounds have largely tightened in recent days, as the presidential races in these states are coin flips.

These battlegrounds are also hosting competitive House races, such as Pennsylvania’s 7th District anchored in Allentown, which is also a presidential bellwether, and the 10th District in Harrisburg, where a former Freedom Caucus leader is on defense.

3. Which issues will win out?

Like the race for president, congressional races have centered on issues that voters often list as crucial to their votes: the economy, immigration, abortion and democracy. But in the waning days of the election, both parties have focused their closing arguments on two distinct issues.

Democratic candidates in the most competitive House and Senate races focused many of their closing ads on abortion, looking to leverage an issue that has boosted the party since the Supreme Court overturned Roe v. Wade more than two years ago. Democrats also believe ballot initiatives enshrining abortion rights in some crucial battlegrounds could boost their candidates, even as polling has shown a wide gap between those measures and Democratic candidates.

The second-most mentioned topic in Democrats’ closing ads last week was immigration, as Democrats look to rebut GOP attacks on the issue, followed by health care, bipartisanship and taxation.

Republicans’ most mentioned topic on the airwaves last week was immigration, often mentioned alongside other topics like transgender women playing women’s sports, as they try to paint Democrats as extreme. Other frequently mentioned topics include Harris, taxation, Biden and character, underscoring how Republicans have tried to nationalize these congressional races.

4. Can Republicans overcome Democrats’ massive financial advantage?

Republicans have long been concerned about Democrats’ massive fundraising advantage in House and Senate races. Democrats saw a fundraising boon when Harris took over the ticket, which flooded down-ballot campaigns with cash as she also broke fundraising records.

That’s allowed Democratic candidates to dominate the airwaves, pushing out their positive messages and launching early attacks against their GOP opponents. While Republicans have gotten a boost from outside groups, those groups are charged higher rates for ads, so their money does not go as far.

Nearly $1.6 billion has been spent on ads in Senate races since Labor Day, with Democrats spending $803 million and Republicans spending $758 million, according to AdImpact.

In each of the competitive Senate contests, the Democratic candidate has outspent their opponent in campaign ads. But Republicans have harnessed big-spending outside groups to take the lead in spending in some key races, like in Ohio’s tight race, where Republicans have spent a combined $185 million to Democrats’ $143 million.

More than $1 billion has also been spent on ads in House races since Labor Day, with Democrats spending $615 million to Republicans’ $448 million, according to AdImpact. And Democratic candidates and outside groups have outspent Republicans in 17 of the 20 House races that have seen the most ad spending this fall.

5. Will there be any surprises?

House and Senate contests could also see some surprise results on election night.

One of the most surprising developments on the Senate map has been a competitive race in Nebraska, where independent Dan Osborn is taking on GOP Sen. Deb Fischer.

The race has led to some late spending in the Cornhusker State, with Republicans looking to prop up Fischer as she tries to close the gap with Trump, who is expected to easily win the state.

Since Labor Day, Osborn has spent $9.8 million on ads and Fischer has spent $3.5 million. And outside groups have ramped up their spending since Labor Day, with independent PAC Retire Career Politicians spending more than $13 million.

Democrats have continued to invest in Texas, where Democratic Rep. Colin Allred is facing GOP Sen. Ted Cruz, and they’re also eyeing a possible pickup in Florida, where former Democratic Rep. Debbie Mucarsel-Powell is challenging GOP Sen. Rick Scott.

Allred has led the race in ad spending since Labor Day, shelling out more than $50 million to Cruz’s $27 million. Senate Majority PAC, the main Democratic outside group involved in Senate races, has contributed $12.2 million in the race so far through its affiliated group WinSenate in an effort to bolster Allred’s campaign by focusing ads on abortion.

In the Maryland Senate race, Republicans have tried to pull off an upset by recruiting former GOP Gov. Larry Hogan to run for the open seat. Hogan has made the race unusually competitive for the typically blue state, but Democratic candidate Angela Alsobrooks has trounced Hogan in ad spending, pouring more than $10 million onto the airwaves, with Hogan spending roughly $3.2 million.

Republicans have ramped up their ad spending in Maryland since Labor Day, thanks largely to the pro-Hogan super PAC Maryland’s Future, which has spent more than $25 million boosting Hogan on the airwaves.