Sen. Joe Manchin III told reporters in his home state of West Virginia on Friday morning that he does not support the bill to make D.C. the nation’s 51st state, according to audio provided by the Democrat’s office and a report from WVNews.

Manchin, a key swing vote in the closely divided Senate, said he believes a constitutional amendment, rather than legislation, would be required to admit D.C. as a state. His stance deals a major blow to statehood advocates who were hoping for his support after the bill passed the House last week.

Manchin cited findings from the Justice Department under Presidents Ronald Reagan and Jimmy Carter and comments from then-Attorney General Robert F. Kennedy in reaching his decision.

“They all came to the same conclusion: If Congress wants to make D.C. a state, it should propose a constitutional amendment. It should propose a constitutional amendment and let the people of America vote,” Manchin said in a radio interview with Hoppy Kercheval of West Virginia’s MetroNews, the full audio of which was provided to The Washington Post by Manchin’s staff.

Manchin was among four in the Senate Democratic caucus who had yet to reveal their positions on statehood; all the other Democratic senators have said they support the idea, but Republicans have been vocally opposed. (One Democrat, Jeanne Shaheen of New Hampshire, co-sponsored a statehood bill in the last Congress but has not signed on as a co-sponsor this year.)

The Washington, D.C. Admission Act passed the House 216 to 208 last week, along strict party lines, for the second time in history. Senate Majority Leader Charles E. Schumer (D-N.Y.) has said that “we will try to work a path to get [statehood] done.”

The bill faces high hurdles in that chamber, with or without Manchin. Because of the Senate filibuster, 60 senators would need to support statehood for the bill to advance — making passage all but impossible as long as the filibuster is in place.

Sen. Thomas R. Carper (D-Del.), the sponsor of the Senate statehood bill, said in a recent interview that he was taking things one step at a time, focusing first on gaining the support of all Democratic senators.

With Democrats in control of the White House and both chambers of Congress, activists say they are in their strongest position yet to make D.C. the 51st state. (Drea Cornejo, Amber Ferguson, Daron Taylor/The Washington Post)

Now that appears unlikely.

Carper spokesman Campbell Wallace said the senator was not available to comment Friday but said in a statement that Carper “remains actively engaged with colleagues on both sides of the aisle and is confident this can reach the finish line by the end of this Congress.”

In a call with reporters that was separate from the radio interview, Manchin said he had not fully developed his opinion before the House voted last week to pass the bill. After that, he said, he and his staff did a “deep dive” on the issue.

He said in the radio interview that he viewed the 23rd Amendment as a chief obstacle for D.C. statehood, echoing arguments from congressional Republicans who have called D.C. statehood unconstitutional. The 23rd Amendment, ratified in 1961, gave D.C. three electoral votes in presidential elections.

Manchin said that Congress had the opportunity to contemplate statehood then but did not go in that direction.

“It complicates D.C.’s path to statehood because Congress had three options to choose from,” Manchin said. “They could have chose statehood back then, retrocession to Maryland . . . or we can grant electoral votes.”

“They chose to grant three electoral votes, which is the same as any small state. That’s where it should be,” he continued. To those who want to change the District’s status, he said, “Let the people of America vote.”

Manchin also cautioned “all of my friends” that if they go down the path of seeking statehood by simple legislation, “you know it’s going to go to the Supreme Court.”

“Every single legal scholar has told us that,” he said. “So why not do it the right way and let the people vote, to see if they want to change?”

Asked whether Manchin supports D.C. statehood in principle, a spokesman said he did not have anything more to add.

Democrats who support statehood say the Constitution does not preclude D.C. from becoming a state. They have framed the debate as a racial-justice and civil rights issue, saying it is immoral to deny the city’s residents voting representation in Congress and the opportunity to fully govern their own affairs.

Stasha Rhodes, campaign director of 51 for 51, noted Friday that every state admitted to the union, including West Virginia, was admitted by Congress. She argued it should not be different for D.C.

“No member of the Senate should deny voting rights to 700,000 mostly Black and Brown Washingtonians based on a flimsy understanding of the Constitution and American history,” she said in a statement.

Del. Eleanor Holmes Norton (D), the District’s nonvoting delegate and sponsor of the House statehood bill, pushed back on Manchin’s concerns over the 23rd Amendment in an interview.

She noted that her bill calls for an expedited resolution seeking repeal of the 23rd Amendment while also immediately repealing the amendment’s enabling clause.

“There are multiple ways to deal with the 23rd Amendment,” Norton said. “We recognize it as an obstacle but nothing like an absolute obstacle.”

She added that Manchin’s position did not surprise her and that “I was never counting on him” to push the bill across the finish line.

“I am counting, however, on getting more Democrats elected so that he does not have the kind of power he now has, by the way, not only over D.C. statehood but over much of the president’s agenda,” Norton said.