Sen. Joe Manchin, a West Virginia Democrat, looks on during a news conference to discuss the national opioid crisis, on Capitol Hill in June 2017 in Washington, DC.
CNN  — 

Former Vice President Joe Biden has signaled an openness to gutting the filibuster to advance the Democratic agenda if he’s elected President and his party retakes the Senate, a move that would squelch the power of the GOP to pare back his ambitions.

But he could have Sen. Joe Manchin standing in his way.

The West Virginia Democrat told CNN that he would oppose his party’s effort to get rid of the filibuster, a stall tactic frequently used by the Senate’s minority party and that requires 60 votes in the chamber to overcome.

“That’s bullshit,” Manchin said this week when asked about the Democratic push to eliminate the filibuster. He noted that he opposed the Democratic effort in 2013 to eliminate the filibuster on most presidential nominees. “And I would be opposed to it again.”

“The whole intention of Congress is basically to have a little bit of compromise with the other side,” Manchin said. “Our job is to find common and cooling ground, if you will, to make something work that makes sense.”

Manchin’s opposition is not insignificant.

To change the rules by using the so-called “nuclear option,” Democrats will need 51 votes. But any Democratic majority in the next Senate will almost certainly be extremely narrow, meaning that losing one or two votes could be enough to scuttle the effort.

Other Democrats are also uncertain whether they would join forces to change the rules, worried that doing so would forever change a body meant to build consensus into one nearly identical to the majority-rules House.

Alabama Sen. Doug Jones, a Democrat who would have to win his tough reelection bid this fall to return next Congress, told CNN he is also opposed to changing the rules to allow legislation to advance on a straight-party vote.

“I think we have to continue to maintain the institutions of the Senate, and the filibuster has long since been an important part of that for the minority, and I would not favor getting rid of that,” Jones said, calling such a move a “slippery slope.”

On Thursday, two other Democrats also indicated they weren’t in favor of eliminating the stall tactic.

“I’ve spoken about this many times before – and I do not believe we should take away the filibuster,” said Sen. Kyrsten Sinema of Arizona.

Sen. Jon Tester of Montana said “I am a no” on changing the filibuster, saying: “The move to make the Senate like the House, I think it’s a mistake.” But he suggested he potentially could change his mind if the GOP were to “stonewall, stonewall, stonewall.”

“I’ll give them more credit than that and say they’re not going to do that; that’s why I wouldn’t throw it away,” Tester told CNN.

Indeed, the debate over eliminating the filibuster has been brewing for years in the institution, which has only intensified under Presidents Barack Obama and Donald Trump. Then-Senate Majority Leader Harry Reid of Nevada and his Democratic majority eliminated the 60-vote filibuster threshold for presidential nominees in 2013 other than for the Supreme Court, prompting howls of protest from Republicans.

Then, after Trump won the presidency, Senate Majority Leader Mitch McConnell employed the nuclear option to eliminate the 60-vote threshold for filibustering Supreme Court nominees, allowing both Neil Gorsuch and Brett Kavanaugh to be confirmed with fewer than 60 votes, infuriating Democrats. McConnell also has pushed through along party lines rules changes to speed up consideration of nominees, allowing him to push Trump’s choices to the bench at a much quicker clip.

Trump has called on McConnell to eliminate the filibuster for legislation, but the GOP leader has resisted doing so, knowing how powerful of a tool that remains for the minority party, which he’s led in the past and could again in the future.

Under the existing rules, senators have to win significant bipartisan support to get legislation through the slow-moving body. That means for any policy measure – whether it’s Biden’s ambitions on health care, climate change or immigration – there must be 60 votes to overcome a filibuster. And if Democrats retake the majority, most believe they will have an extremely narrow advantage or may even control a 50-50 Senate.

But given the highly polarized body, most believe that no major legislation would move through in a Biden presidency, which is why calls are growing to eliminate the filibuster’s 60-vote threshold altogether.

Sen. Amy Klobuchar of Minnesota, the ranking Democrat on the Senate Rules Committee, said she’s “open to it and considering it” and she’d vote for the rules change if Republicans “are just blocking major pieces of legislation that we cannot just wait anymore for as a country.”

“We have to have such a momentous session next year,” Klobuchar said this week. “We’re going have to do more on the pandemic. All of these things like minimum wage, climate change, that have been sitting around with no action for years and so I’ve always said during the presidential campaign that we should consider it but it should be leverage.”

Added Colorado Sen. Michael Bennet: “We cannot go through another 10 years here like the last 10 years.”

The effort to change the rules would be led by Sen. Chuck Schumer, the New York Democrat poised to become majority leader if Democrats pick up at least three seats in November, assuming Biden wins the presidency since the vice president breaks a tie in the chamber.

Schumer has for months declined to say what his view is on the consequential matter – but has pointedly left it on the table.

“Job No. 1 for us is to get the majority. We don’t take anything for granted, but it’s looking better and better,” Schumer told reporters Tuesday when asked if he supports gutting the filibuster. “Once we get the majority, we’ll discuss it in our caucus.”

Senate Minority Whip Dick Durbin, Schumer’s No. 2, sounded open to changing the rules and pushed back on the concerns that the body would be forever changed.

“This institution’s been changed forever by Mitch McConnell, make no mistake,” Durbin said, referring to McConnell holding a Supreme Court seat vacant during Obama’s final year in office and then gutting filibuster rules for high court nominees. “So let’s be honest. This is not the Senate that I was elected to, and it’s not the Senate most people read about when they study the Constitution.”

Durbin added: “The question is how can we make this Senate functional and fair in the future.”

This story has been updated with additional developments Thursday.

CNN’s Ian Sloan, Cat Gloria and Ali Zaslav contributed to this report.