WASHINGTON >> Sen. Joe Manchin, the conservative West Virginia Democrat who has said he will retire at the end of his term, today switched his party registration to independent, the final step in a yearslong breakup with his party that left open the possibility of another run for office.

Manchin has said he will not run for reelection to the Senate or for governor — a role he previously held for two terms — but rumors persist on Capitol Hill that he could change his mind.

West Virginia’s deadline for independent candidates to declare their candidacies is not until Aug. 1. Since Manchin said he would not run again, Sen. Chuck Schumer, D-N.Y., the majority leader, has been pleading with him to formally leave the Democratic Party and seek reelection as an independent.

If he did so, Manchin would face Jim Justice, a Democrat-turned-Republican second-term governor with whom he has a storied rivalry. Justice is popular in the state, and his decision to enter the Senate race was seen as a key factor in Manchin’s decision not to seek reelection. His plan to exit all but guarantees that Democrats will lose the seat in November, putting their already razor-thin hold on the Senate in peril.

Manchin has long threatened to leave the Democratic Party as it has shifted to the left. He has frequently complained that there is no room in the Senate for centrists like him, famously telling colleagues, “This place sucks.” But he has also consistently said he does not see himself as a Republican and has been highly critical of former President Donald Trump and his brand of polarizing politics.

“Since becoming a United States senator in 2010, I have seen both the Democrat and Republican parties leave West Virginia and our country behind for partisan extremism while jeopardizing our democracy,” Manchin said in a statement today. “Today, our national politics are broken and neither party is willing to compromise to find common ground. To stay true to myself and remain committed to put country before party, I have decided to register as an independent with no party affiliation and continue to fight for America’s sensible majority.”

In switching his party affiliation, Manchin joins three other senators who caucus with the Democrats but are registered independents: Kyrsten Sinema of Arizona, Bernie Sanders of Vermont and Angus King of Maine.

As a Democrat from a deeply Republican state, Manchin has been a constant source of attention on Capitol Hill. He repeatedly frustrated his fellow Democrats by breaking with them on progressive legislation, dooming some of their top priorities in a nearly equally divided Senate. But he is also known for helping broker deals that resulted in some of the most significant new laws during Biden’s presidency, included passage of the biggest investment in clean energy in U.S. history.

Manchin was sworn in as a senator in 2010, after winning a special election to serve out the remainder of the term of Sen. Robert C. Byrd, the long-serving pillar of the Senate, who had died at the age of 92. His houseboat, named Almost Heaven, has served as a hangout for senators in both parties.

This article originally appeared in The New York Times.