Liberals hoping to abolish the filibuster have more than just Sen. Joe Manchin III (D-W.Va.) standing in the way of unlocking the most ambitious phase of their legislative agenda.

Manchin may be the most outspoken Democratic defender of the Senate’s 60-vote supermajority requirement, but even if the legislative filibuster got abolished tomorrow, Democrats would struggle to pass some of their highest-profile items, while others would remain nonstarters.

That’s because, if the anti-filibuster advocates succeed abolishing that procedural hurdle, they would need all 50 members of Senate Majority Leader Charles E. Schumer’s caucus to support legislation and then have Vice President Harris break the tie in their favor.

And Manchin, along with quite a few other Democrats, has deep reservations about the most ambitious pieces of that agenda.

He has already declared he is not going to support a voting rights bill that House and Senate Democrats have otherwise declared their highest priority, and he has expressed opposition to the House-passed legislation to increase background checks on gun purchases.

Sen. Richard J. Durbin (D-Ill.), chairman of the Judiciary Committee, recently declared that President Biden’s comprehensive overhaul of immigration laws lacked sufficient Democratic support to pass the House, where Speaker Nancy Pelosi (D-Calif.) can afford just three defections from her ranks to pass an all-Democratic bill.

The effort to create a $15 minimum wage fell on its face when just 42 Senate Democrats voted for the proposal during an amendment vote last month.

That’s the same number of co-sponsors Democrats have for legislation that would grant statehood to the District of Columbia, a move that would very likely lead to two Democrats getting elected to the Senate. Support for expanding the Supreme Court, a liberal dream following President Donald Trump’s success in confirming three justices to secure a conservative majority, lags far behind D.C. statehood’s level of support.

And Medicare-for-all, the single-payer health insurance proposal, had just 15 co-sponsors in the Senate last year.

Simply put, in the words of some advisers to Senate Democrats, counting to 50 is hard. And even if they do move to a simple majority, Democrats might end up advancing important-but-incremental proposals that are not the grand ideas that dominated the presidential primary debates last year.

This reality has created a split screen for the Democrats, where inside the Capitol there is lingering doubt about ending the filibuster because no one is certain what will actually pass if a simple majority rules the day.

Yet beyond Capitol Hill, the vast array of party apparatus is moving forward with the expectation that Schumer (D-N.Y.) will be able to round up 50 votes to blow up the filibuster on a party-line vote, with Harris breaking the tie. People from large donors to former president Barack Obama, along with powerful unions and civil rights leaders, support the move.

Even Biden, a 36-year veteran of the Senate, has opened the door to some changes in filibuster rules.

“It is every element of the Democratic coalition,” said Adam Jentleson, former deputy chief of staff to former Senate Democratic leader Harry M. Reid (Nev.).

Jentleson, who wrote “Kill Switch,” a book about the filibuster as a “crippling” force, described Democratic senators as a “lagging indicator” of where the party is heading and predicted that eventually they will fold amid intense pressure from their own supporters.

“All the incentives are pulling in the same direction,” he said.

This creates a few strategic questions that are percolating through the minds of top Democratic aides and some senators: What legislation will actually become law if they blow up this Senate tradition? What proposal is worth the move? And will Democrats further disappoint their own supporters if they still can’t approve their most muscular liberal agenda on a simple majority?

The two most likely bills to get approved in a simple-majority Senate are the Dream Act, which would grant permanent status to millions of undocumented immigrants who were brought to the United States as children, and the John Lewis Voting Rights Act, which is named after the late Georgia congressman and would update the landmark 1965 civil rights law.

Every member of Schumer’s caucus co-sponsored the voting act last year, including Manchin, so it would almost certainly have enough support to pass on a simple majority. And Durbin has already said that he has every Democrat supporting the Dream Act and is close to securing 10 GOP votes needed to clear a filibuster under current rules.

“I’ve been stopped by the filibuster five times from passing it. I had a majority; I didn’t have 60 votes. Do I have 60 now? I think I’m close,” Durbin, who is the majority whip, said on CNN’s “State of the Union” last month.

Liberals believe they would probably have a united Democratic front to add judgeships to the lower federal courts around the nation, if they just need 50 votes from Schumer’s caucus. Even Chief Justice John G. Roberts Jr. has supported this in the past.

But these narrower proposals do not animate the left.

Most immigration advocates want a comprehensive bill that will deal with all undocumented immigrants, not just those brought here as children, and Democrats have rallied behind the For the People Act, with its expansive proposals mandating early voting and mail-in ballots along with creating nonpartisan commissions to draw congressional district lines.

And they want to expand the Supreme Court, not lower courts.

How would Biden’s supporters react if Democrats took the bold action of eliminating the “Jim Crow relic,” as Obama labeled the filibuster, and still only passed compromise measures within their own ranks?

When Manchin suggested removing some portions of the For the People Act, activists lashed out. “There is absolutely no reason for supporters of S. 1 to negotiate with ourselves and dramatically narrow the reforms in the bill,” wrote Fred Wertheimer, president of Democracy 21.

Even with the filibuster still alive, Democrats have moved quickly to advance a sweeping portion of Biden’s agenda. First was a $1.9 trillion pandemic relief bill, and next up is a jobs package that could total $4 trillion in the fall.

The first bill used budget procedure rules that allowed a simple majority to push it through the Senate, something Democrats are almost certain to try again for the second package.

Jentleson sees these budgetary bills as the gateway drugs to procuring the final votes of support to end the legislative filibuster, from Manchin and roughly 10 others who have expressed hesitation.

“Why not,” he asked, “just keep doing this?”