David McCormick Will Enter Pennsylvania Senate Race, One of 2024’s Biggest

David McCormick, a former hedge fund executive who lost the Republican primary for Pennsylvania’s open Senate seat last year, is set to announce on Thursday that he is running again for Senate — this time against Senator Bob Casey, a Democrat.

Mr. McCormick will begin his campaign with a speech in Pittsburgh, according to two people familiar with the conversations.

An Army veteran and former Treasury Department official, Mr. McCormick will enter one of the country’s most closely watched Senate races.

Long a battleground state, Pennsylvania has tilted toward Democrats in recent years, and Republicans faced several losses in 2022. Mr. Casey, 63, who was first elected to the Senate in 2006, has the advantage of incumbency and a hefty fund-raising haul. The Cook Political Report, a nonpartisan newsletter, describes the race for his seat as leaning Democratic.

Still, Republicans see the seat as a potential pickup, with Democrats trying to defend a thin Senate majority while facing difficult races for their incumbents in West Virginia, Ohio and Montana. All three states have voted for former President Donald J. Trump and other Republicans in the last several elections.

One of the biggest differences for Mr. McCormick in his second run for Senate is that, at least so far, no other Republicans have entered the race.

Party leaders and major Senate fund-raisers have indicated that they will back Mr. McCormick. In another potential boost to his candidacy, Doug Mastriano, a Republican state senator who lost the governor’s race in Pennsylvania last year and was seen as a possible contender in the 2024 Senate contest, announced in May that he would not run.

Democrats have similarly coalesced around Mr. Casey, which has so far helped mask turmoil inside the state party.

During the 2022 midterm cycle, Mr. McCormick ran for the seat held by the retiring Senator Pat Toomey, a Republican, but he lost the primary by 950 votes to Dr. Mehmet Oz. Mr. Oz, who was endorsed by Mr. Trump, was swept aside in November by John Fetterman, a Democrat whose victory helped his party maintain its narrow control of the Senate.

Since his loss in June last year, Mr. McCormick has remained politically active in the state, attending local party events and embarking on a book tour. He started a political group, Pennsylvania Rising, to support G.O.P. candidates and tackle “the challenges facing Pennsylvania Republicans” — though the apparatus has been seen as a possible tool to help his long-expected bid.

Mr. McCormick has also faced scrutiny over whether he resides in Pennsylvania: Last year, he moved there from Connecticut to run for Senate. The Associated Press reported last month that while he owns a home in Pittsburgh, public records showed that he still lived in and rented a $16 million mansion in Westport, Conn.