HARRISBURG (AP) — Democratic U.S. Sen. Bob Casey and Republican David McCormick will be the only eligible names on ballots for the office in Pennsylvania’s April primary after a ruling Friday by the state’s highest court.

The ruling completed the third of three successful court challenges to the paperwork of three relatively unknown candidates, all but guaranteeing uncontested victories for Casey and McCormick in their respective party primary elections on April 23.

The November contest between Casey and McCormick is expected to be one of the nation’s most expensive and closely watched in a year when Democrats have a difficult 2024 Senate map that requires them to defend incumbents in red states and multiple swing states.

Casey is running for a fourth term against McCormick, a former hedge fund CEO who is endorsed by the state Republican Party and narrowly lost the 2022 GOP primary to Dr. Mehmet Oz.

The presidential battleground state of Pennsylvania will be critical to whether Democrats can maintain control of the White House and the Senate, and a Casey loss would likely guarantee Republican control of a Senate currently divided by the narrowest of margins.

The state Supreme Court rejected an appeal from a Republican candidate, Joe Vodvarka, who had been ordered off primary ballots by a lower court that found he had not received enough voter signatures to qualify.

Vodvarka had appealed, arguing that he must be allowed onto primary ballots because the Republican voters who had challenged his petitions had not advised the state elections office of their legal challenge, as they are required to do by law. The state Supreme Court, in its two-line order, did not explain its decision.

Courts earlier in March had already granted challenges to the paperwork of two other candidates filing for the primary ballot for U.S. Senate.

Both Brandi Tomasetti, a Republican from Lancaster County, and William Parker, a Democrat from Allegheny County, were ordered off ballots.