Republicans have flipped a Senate seat in Pennsylvania, padding their new majority in the chamber and sending longtime Democratic incumbent Bob Casey packing.

Republican Dave McCormick rode Donald Trump's coattails to a shocking upset against Casey, a fixture in the state's politics who has been in the Senate since 2007.

Upset in Pennsylvania

With McCormick's win, Republicans now have a 53-seat majority in the Senate, leaving President-elect Trump with additional leverage to enact his "Make America Great Again" agenda starting in January.

Casey, the son of a former Pennsylvania governor, had never been on the same ballot as Trump until this year. Trump won Pennsylvania - the biggest prize among the battlegrounds - by 2 points, securing his path back to the White House.

Trump's win pulled McCormick to a narrow victory of less than a percentage point. While the AP has called the race for McCormick, Casey has not conceded, pointing to provisional ballots.

"Pennsylvania is where our democratic process was born. We must allow that process to play out and ensure that every vote that is eligible to be counted will be counted. That is what Pennsylvania deserves," Casey said.

McCormick's team is challenging provisional ballots in Philadelphia - a notoriously corrupt Democratic stronghold - and vowing to go to the Supreme Court if necessary, as Democratic operative and election lawyer Marc Elias declares the race "not over."

Senate control flips

McCormick, an Army veteran, former CEO of the world's largest hedge fund and alumnus of the George W. Bush administration, had early backing from the Republican party during the primary.

McCormick ran in the Republican primary in 2022 for Democrat Pat Toomey's Senate seat, with McCormick losing to Dr. Oz. Republicans fell short that year as Oz lost to Democrat John Fetterman and a much-anticipated red wave fizzled nationwide.

Pennsylvania shifted rightward with the entire nation this year as President Trump secured a historic second, non-consecutive term with a popular vote victory.

Republicans Bernie Moreno, Tim Sheehy, and Jim Justice secured the Senate for the GOP with wins in Ohio, Montana, and West Virginia, respectively.

Democratic Senate incumbents Jacky Rosen in Nevada and Tammy Baldwin in Wisconsin have secured re-election, and Democratic Rep. Elissa Slotkin won an open seat in Michigan. Arizona's Senate race between Trump-backed Kari Lake and Ruben Gallego has not been called.