When Democratic Sens. Raphael Warnock and Jon Ossoff both won their Senate runoff races in Georgia on Jan. 5, they handed Democrats full control of government in Washington for the first time since 2010. But Democrats hold the Senate by only the slimmest possible margin: a 50-vote tie that could be broken by Vice President Kamala Harris .

If President Joe Biden and congressional Democrats want to pass their sweeping agenda, they are going to have to change the Senates filibuster rules.

Support for reform is growing. As of April 2, there were 27 Senate Democrats who openly supported either ending or reforming the chambers filibuster rules for legislation, according to a HuffPost review of statements. An additional 19 remain open to reforming or repealing Senate filibuster rules. But there are at least three senators Joe Manchin (D-W.Va.), Kyrsten Sinema (D-Ariz.) and Pat Leahy (D-Vt.) who continue to state that they do not want to change the Senates 60-vote threshold. (The position of Democrat Maria Cantwell of Washington is currently unknown.)

They will need all 50 Democratic Party caucus members to change the rules.

Check out more on Democratic senators positions above.

Under current Senate rules, it takes 60 votes to end debate on a bill and overcome a filibuster. This is called a cloture vote. For Democrats to defeat any filibuster, they would need 10 Republicans to defect to vote to end debate. But Republicans already refused to provide votes for Bidens $1.9 trillion COVID-19 relief package, a sign that they will move back into the position of total opposition they occupied during President Barack Obama s first two years in office. Theyre almost certain to do the same for legislation on voting rights, gun control, immigration and more. And so Democrats may need to change Senate rules to get their agenda enacted.

Many key senators who now support or are open to changing filibuster rules have loosened their previous opposition to changing the filibuster. Twenty-one out of 25 Democrats who signed a bipartisan letter supporting the filibuster in 2017 have since changed their minds. Those who have changed their position point to Republican refusal to work on the American Rescue Plan and the apparent return of Senate Minority Leader Mitch McConnells redeployment of the all-out obstruction plan he used to stymie Obamas agenda.

I dont want to turn away from Senate traditions, but I also dont believe one party should be able to prevent votes on important bills by abusing the filibuster, Sen. Dianne Feinstein (D-Calif.), a longtime filibuster supporter, said on March 19 .

If ... the minority hangs together and regularly uses this power to block any and all initiatives of the majority (and their president), supporting the continuation of the rule becomes harder and harder to justify, regardless of the long-term consequences, Sen. Angus King (I-Maine), who signed the 2017 letter, said in a March 24 opinion article in The Washington Post .

The onus is on Senate Minority Leader McConnell, Sen. Jack Reed (D-R.I.), another 2017 letter signatory, said in January . He can either be a constructive part of that effort or create a wall of partisan obstruction and further threaten the Senates traditions.

Like these senators, Biden shifted his stance from support for the current filibuster rules to an openness to reform in pointed remarks at a March 25 press conference .

My Republican colleagues are going to have to determine whether or not we want to work together, or decide the way in which they want to proceed is to just divide the country, Biden said. Im just going to move forward and take these things as they come.

McConnells use of the filibuster will come up soon as a raft of bills passed by the House piles up in the Senate.

One of the most notable bills is the For the People Act, which expands voting rights, bans gerrymandering and reforms campaign finance, among other things, and has received the top legislative designations of H.R. 1 and S. 1 by Democrats in both chambers. The bill passed in the House on March 3 and is now moving through the committee process in the Senate. It is expected to receive a floor vote, when Republicans are expected to block it with a filibuster.

We will see if our Republican friends join us. If they dont join us, our caucus will come together and decide the appropriate action to take, Senate Majority Leader Chuck Schumer (D-N.Y.) said upon introducing the bill in the Senate. Failure is not an option.

Schumer will need to convince holdouts like Manchin, Sinema and Leahy to drop their opposition to changing the filibuster rules. Manchin has suggested some openness to bringing back the so-called talking filibuster. But he has also stated a contradictory position of not wanting to change the 60-vote threshold.

Im still at 60 .. I havent changed, Manchin said on March 17 .

On April 7, Manchin further underlined his opposition to changing filibuster rules in an opinion piece in The Washington Post .

There is no circumstance in which I will vote to eliminate or weaken the filibuster, Manchin wrote.

In a letter to a constituent, Sinema asserted her opposition to changing the filibuster rules: I have long said that I oppose eliminating the filibuster for votes on legislation.

Meanwhile, Leahy, the longest-serving member of the Senate, stated in 2019 that he opposes changing filibuster rules. I agree with Thomas Jefferson, he said. [The Senate] is the cooling saucer where things cool. He has not stated any change in position since, and, when asked whether he has changed his position, his office offered, No further comment at this time.

This position of opposition may be strongly held or it could be contingent. In 2013, Republicans used the filibuster to block numerous Obama judicial appointees, particularly to the U.S. Court of Appeals for the District of Columbia Circuit, the second most important federal bench after the U.S. Supreme Court. Harry Reid, then the Senate majority leader, pushed to end the filibuster for non-Supreme Court seats. Many Democrats claimed opposition to doing so for months. That is, until they didnt.

The same may come true for the legislative filibuster as Senate Republicans begin to block passage of legislation.