Bernie Sanders has said he may consider supporting primary challengers against colleagues Joe Manchin and Kyrsten Sinema, the two Democrat holdouts in debate over whether to amend the filibuster to pass voting rights legislation.

The progressive Vermont senator told reporters on Tuesday that he believes “there is a very good chance” that Manchin, a West Virginia Democrat, and Sinema, a Democrat from Arizona, will face primary challenges because of their stance on the filibuster.

He said home-state voters would be disappointed that the pair have refused to support changing Senate rules to overcome a Republican filibuster against major voting legislation while also balking at the massive, Biden-backed spending and social plan known as Build Back Better.

When asked if he would consider backing such primary challengers, Sanders replied, “Well, yeah.”

Sanders, an independent who caucuses with Senate Democrats, didn’t elaborate on his comment, but it is unusual for senators to suggest they would be willing to campaign against colleagues from their own party.

Sanders’s sentiments also lay bare progressives’ growing frustrations with the more conservative senators, Manchin and Sinema, whom the left has blamed for stalling many of Biden’s top legislative priorities.

Manchin and Sinema say they support the legislation but are unwilling to change Senate rules to muscle the legislation through the chamber over Republican objections. With a 50-50 split, Democrats lack the 60 votes needed to overcome the Republican filibuster.

Manchin is expected to deliver a floor speech on Wednesday afternoon outlining his position on changing chamber rules to allow voting rights legislation to move forward. Yesterday he countered Sanders’s comments, saying he would not be bothered by a primary challenger.

“I’ve been primaried my entire life. That would not be anything new for me,” he said Tuesday, when asked about fellow Democrats urging voters not to back him in a primary. “I’ve never run an election I wasn’t primaried. This is West Virginia, it’s rough and tumble. We’re used to that. So bring it on.”

Sanders remains one of the nation’s leading progressive voices after strong Democratic presidential primary bids in 2016 and 2020 – and is still popular enough nationally to potentially affect Senate primaries around the country.

Manchin and Sinema are not up for re-election until 2024, but both could face serious primary challengers then. Democratic representative Ruben Gallego of Arizona, who has sharply criticized Sinema for not supporting the voting rights legislation, has not ruled out launching a challenge against her.

Manchin and Sinema are also experiencing some external pressure as they resist efforts to change the filibuster to pass voting rights legislation. Emily’s List, the progressive group that backs female candidates who support abortion rights and has deep ties to Democrats, said it would withhold its endorsement from Sinema because of her stance on filibuster reform.

“Our mission can only be realized when everyone has the freedom to have their voice heard safely and freely at the ballot box,” Emily’s List’s president, Laphonza Butler, said in a statement released on Tuesday.

Naral Pro-Choice America, which supports abortion rights and is also influential in top Democratic circles, released its own statement suggesting it would no longer support or endorse Manchin or Sinema because of their stances on the legislation.

The voting rights legislation in question is the Freedom to Vote: John R Lewis Act, which civil rights activists say is vital to safeguarding American democracy as Republican-led states pass new restrictive voting laws. It would make election day a national holiday while ensuring access to early voting and mail-in ballots – both of which have become especially popular during the Covid-19 pandemic. The package also seeks to let the justice department intervene in states with a history of voter interference, among other changes.

• Associated Press contributed to this report