The battle over Supreme Court Justice Brett M. Kavanaugh’s confirmation threw a wildcard into the race for Senate control. But the contours of the fight for the chamber aren’t much different from a year ago: Democrats running for re-election in states President Donald Trump carried by wide margins in 2016 are in trouble heading into Election Day.

Democrats are defending 26 seats — 10 of them in states that backed Trump — while Republicans are only defending nine. Given that imbalance, it’s no surprise that Trump’s effect on Senate races has been different from his influence on the fight for control of the House, where he’s put GOP incumbents on defense.

Here are five defining elements — including a few surprises — that have shaped where we are on Election Day.Watch: How We Got Here — The Biggest Surprises in a Campaign Season for the Ages

1. The Alabama special election

Democratic odds of retaking the Senate would have been more daunting without Roy Moore. The former Alabama Supreme Court chief justice was on course to win last December’s special election to fill Attorney General Jeff Sessions’ Alabama Senate seat until The Washington Post broke the story about him making inappropriate sexual advances toward teenagers when he was in his 30s.

The White House and the Republican National Committee’s decision to stand by Moore tarnished the GOP in some voters’ minds. But more significantly for the battle for the Senate, Democrat Doug Jones won. And his victory cut the number of seats Democrats need to flip from three to two.

2. Trump loyalty contests

As demonstrated by the Alabama Senate result, former White House adviser Steve Bannon hasn’t lived up to his own hype. He’d promised to give every Senate Republican, except Texas’ Ted Cruz, a primary race. But primaries against Senate GOP incumbents were a nonissue this year. (House Democrats got a taste of that anti-incumbent tension instead.)

That doesn’t mean Republicans were without internecine warfare or anti-establishment fervor, though. West Virginia, Indiana and Arizona saw three of the nastiest Senate primaries, with three Republicans in each state duking it out in Trump loyalty contests.

Arizona Rep. Martha McSally defeated two Trump loyalists in her primary: controversial former Maricopa County Sheriff Joe Arpaio and former state Sen. Kelli Ward. She received a boost from establishment Republicans, but some in the party believe that money might have been better spent attacking the Democratic nominee, Rep. Kyrsten Sinema, who got a head start on the airwaves while Republicans fought it out until late August.

West Virginia Republicans also battled over who was most loyal to Trump (and who was a closet Hillary Clinton supporter). Democrats attacked GOP Rep. Evan Jenkins, whom they thought would give incumbent Joe Manchin III his toughest challenge. After dodging Don Blankenship, Republicans ended up with state Attorney General Patrick Morrisey, who ran as an anti-Washington outsider in the primary but hasn’t been able to land those punches as successfully against Manchin, who’s slid down the list of most vulnerable senators.

In Indiana, GOP nominee Mike Braun dispatched two rival congressmen in the primary by touting himself as a businessman outsider just like Trump. Inside Elections with Nathan L. Gonzales rates his general election race against Democratic Sen. Joe Donnelly a Toss-up. Trump’s 2016 margin in the Hoosier State, combined with Donnelly’s vote against Kavanaugh, could tip the scales for Braun. But if the Republican loses Tuesday, it’ll be another reminder of how difficult it is for a GOP candidate who is not Trump to replicate his success.

3. Shifting battlefield 

Several other Republican nominees have already discovered that. Pennsylvania Rep. Lou Barletta and Ohio Rep. James B. Renacci both embraced the president early on in their Senate races, but neither stands much chance of winning in states that backed Trump in 2016.

The fact that Ohio and Pennsylvania (both home to expensive 2016 Senate races), Wisconsin, and Michigan never developed into top-tier races significantly altered the battlefield by almost cutting in half the number of seats Democrats needed to defend. That freed up national resources for expensive states like Florida, where despite spending millions of dollars of his own money, GOP Gov. Rick Scott has not been able to put his race against Democratic Sen. Bill Nelson away. It also meant national Democrats had money to throw at New Jersey, where a Republican self-funder has made the race more competitive than it should be in a blue state.

National Republicans, meanwhile, have been forced to spend in two unexpected states. Former Democratic Gov. Phil Bredesen has given GOP Rep. Marsha Blackburn a real race in Tennessee, while Texas Democratic Rep. Beto O’Rourke’s fundraising has put Cruz on defense.

4. Health care, health care, health care 

As they have all year, Democrats at both the House and Senate levels have been almost singularly focused on health care. After failing to pass their plan to repeal the 2010 health care law, Republicans turned to the tax overhaul as a legislative achievement they could tout on the campaign trail. But Senate Democrats got more health care ammunition when Republican attorneys general (two of whom also happen to be running for Senate) signed on to a Texas lawsuit against the 2010 law. At the very least, it gave Manchin another object to shoot at, which makes for good television in West Virginia.

5. Kavanaugh craziness 

The allegations that Kavanaugh sexually assaulted Christine Blasey Ford when they were teenagers and the subsequent hearings energized both the left and the right, the net effect of which is still to be determined.

Many of the most competitive Senate races have tightened this fall. And it’s difficult to determine causality — some of that could be Republicans naturally tuning in late — but the hearings certainly contributed to a greater nationalization of these races.

Nationalized races benefit Republicans at the Senate level. (The opposite is true at the House level.) Republican strategists credit the White House for getting Trump out on the trail repeatedly in places like Montana, for example, where the GOP nominee would likely lose a localized race to Democratic Sen. Jon Tester.

“This will be an election of Kavanaugh, the caravan, law and order and common sense,” Trump said last month at a Montana rally for Tester’s opponent, state Auditor Matt Rosendale.

Republicans running for Senate hope he’s right. But that may come at the expense of their colleagues in the House.

Bridget Bowman contributed to this report.