Control of the US Senate is on the line tonight as early vote totals come in the race between Democratic incumbent Sen. Bob Casey and Republican challenger Dave McCormick.

Casey is one of five Senate Democrats who are considered vulnerable in this election, and Republicans only need to flip one or two of those seats to gain control of the chamber. Even if one party wins a majority in the US House of Representatives and the presidency, each party will need support in the Senate to approve executive appointments and fill judicial vacancies, including any vacancies that arise on the US Supreme Court.

Because of the key role the justice plays, the issue of abortion played a prominent role in the campaign following the Dobbs decision that overturned abortion rights in 2022. The economy and immigration were also important — but sometimes overshadowed by the candidates’ personal attacks on the files of the other.

McCormick sought to portray Casey as a do-nothing politician who served 18 years in the Senate and had few legislative victories. Casey attacked McCormick for running a wealthy investment fund that sometimes invested in China and for giving a misleading picture of his track record as CEO of a Pittsburgh company.

Casey has led the polls since the race began, but in the last two months of the election, the polls have tightened within the margin of error in many polls, and the Cook Political Report rated the race a disappointment. While a few polls showed McCormick in the lead, dozens of polls showed Casey still holding a slim lead.

In the early days of the race, Casey attacked McCormick for spending most of his time with his family in Connecticut. But as McCormick had more time to explain his childhood and work experience in Pennsylvania, the arguments in the race shifted to specific issues.

Casey’s campaign emphasized the issues McCormick’s campaign attacked. Casey ran ads saying he was tough on the border and wanted to pass a bipartisan border security deal, even picturing himself next to the border wall. Casey has also spent months talking about his plans to crack down on corporations for raising prices to curb inflation.

Abortion was the main issue Casey used to attack McCormick. By the end of the campaign — including an appearance in Wilkinsburg on Friday — Casey appeared alongside abortion groups and advocates who said abortion rights were at stake.

“It’s not a theory or a constitutional debate about the finer points of the law,” Casey said Friday, standing next to two women who cited personal experiences and said Republican abortion laws would leave them vulnerable. “It’s about human beings, about women living in a different world than the one we lived in a few years ago.”

McCormick said his background as a CEO and military veteran gave him a special perspective on the economy and foreign affairs. In western Pennsylvania, McCormick emphasized the need to support the natural gas industry and attacked the Biden administration for considering the industry’s future limits. And McCormick said threats from China and Russia mean the country must make a massive increase in military spending.

Neither Casey nor McCormick highlighted major areas of disagreement with their party, with a few notable exceptions. McCormick supports Ukraine’s war effort in a way that contrasted with Trump’s statements about his war with Russia. Casey has at times urged the Biden administration to do more to support the local natural gas industry, particularly in terms of exporting natural gas and supporting hydrogen power that can be produced with local natural gas.

Still, McCormick made a last-ditch appeal to Republicans uncomfortable with Donald Trump, tangling with former U.S. ambassador to the United Nations and South Carolina Gov. Nikki Haley last week. Haley and Trump did not campaign together after a bruising primary battle. Haley said support for Trump is essential to McCormick.

“Dave McCormack can’t win if we don’t elect Donald Trump at the top of the ticket,” Haley said. “You may find Trump loud, but what I will tell you is that he understands that we have to turn this economy around.”

The candidates faced off for two debates, in which they often turned to attacking each other rather than laying out their own legislative visions. They rarely varied from the fixed lines they used in their advertisements and speeches.

Although Casey’s campaign spent more money on ads than McCormick’s campaign, the Republican challenger was backed by outside money and overall outspent Casey by about $5 million in a race where more than 350 millions of dollars just for advertising.

Casey hasn’t had to win a Democratic primary in recent years and has been able to shift to a more progressive stance on issues like abortion without creating a major fight within his own party. McCormick lost a close primary against Oz in 2022 and had to distance himself from some of his statements on abortion in that race.

Other Senate races that could result in control of the Senate are in Montana, Ohio, Arizona, Nevada and Michigan. Republicans are all but certain to take U.S. Sen. Joe Manchin’s seat in West Virginia, but Democrats have some hope they could flip a seat in Texas or Nebraska, where independents are running strong races.