WASHINGTON — If Democrats eradicate the filibuster, there’s one senator who would have an outsized influence within the 50-50 chamber on points that might reshape the nation’s future: infrastructure, immigration, gun legal guidelines and voting rights. That senator is Joe Manchin III of West Virginia.

There may be additionally a senator whose opposition to eliminating the filibuster is a big cause it could by no means occur. That senator, too, is Mr. Manchin.

“He ought to need to do away with the filibuster as a result of he immediately turns into essentially the most highly effective individual on this place — he’s the fiftieth vote on every part,” mentioned Senator Chris Coons, Democrat of Delaware, sketching out, although not embracing, the argument.

Mr. Manchin, nonetheless, doesn’t see it that manner. To the exasperation of Democrats, delight of Republicans and bewilderment of politicians who can’t perceive why he wouldn’t need to wield extra energy, Mr. Manchin isn’t budging.

“Sixty votes,” he mentioned in an interview final week in his workplace, referring to the brink required to advance most laws, including that he wouldn’t think about suspending the filibuster for sure payments, as a few of his colleagues have floated: “You’re both dedicated or not.”

However with 18 individuals lifeless after two mass shootings inside per week, a worsening migrant problem on the border and Republicans attempting to limit voting in nearly each state the place they maintain energy, liberals consider this second cries out for a unique kind of dedication. At a time once they have full management of Congress and are confronting overlapping crises, many Democrats really feel an ethical and political crucial to behave, course of be damned.

That places Mr. Manchin, 73, on the middle of crucial coverage debates in Washington — and has set the stage for a collision between a celebration keen to make use of its majorities to go sweeping laws and a political throwback decided to revive bipartisanship to a chamber that’s as polarized because the nation.

Mr. Manchin believes that ending the legislative filibuster would successfully destroy the Senate. He recalled his predecessor, Robert C. Byrd, telling him that the chamber had been designed to drive consensus.

Mr. Manchin has expressed willingness to help a “speaking filibuster,” through which lawmakers have to really maintain the ground, maybe for a lot of hours, to dam a vote. However he has not yielded on eliminating it altogether and on an array of points, together with voting rights and gun management, his admonition is much less about any specific coverage finish and extra about ensuring the laws has help from each events.

Extra broadly, Mr. Manchin’s resistance to ending the filibuster has ripened elementary questions on which model of Congress could be extra dysfunctional: a physique stymied by gridlock or one that may go laws solely by scrapping longstanding pointers so it may push by means of party-line votes?

“You may’t make the place work if nothing vital is getting handed,” mentioned Consultant Ro Khanna, a number one progressive from California.

Mr. Manchin worries that the short-term good thing about ditching the filibuster would backfire for Democrats over the long run.

“I’m involved concerning the Home pushing an agenda that might be exhausting for us to take care of the bulk,” Mr. Manchin mentioned concerning the progressive laws that Home Democrats are stacking up on the Senate door. As for strain from the left, he mentioned, tauntingly: “What are they going to do, they going to enter West Virginia and marketing campaign towards me? Please, that might assist me greater than something.”

To a rising variety of his Democratic colleagues — and never simply liberals — it’s naïve to maintain placing hope over historical past, and consider, as Mr. Manchin mentioned about gun laws, that Republicans could say, “Hear, it’s time for us to do the cheap, smart factor.”

After all, few in a Senate that will depend on Mr. Manchin for a fiftieth vote will say outright that their colleague is indulging in fantasy.

“Joe’s focus, I consider, is bipartisanship, and I agree with the start line,” mentioned Senator Richard J. Durbin of Illinois, earlier than reducing the growth: “They weren’t going to present us a single vote,” he mentioned concerning the stimulus invoice.

A former highschool quarterback who pals say nonetheless relishes being on the middle of the motion, Mr. Manchin is one thing of a unicorn in as we speak’s Congress. As a pro-coal and anti-abortion Democrat, he displays a less-homogenized period when regionalism was as vital as partisanship and senators have been extra particular person actors than predictable votes for his or her caucus.

Twice elected governor earlier than claiming Mr. Byrd’s seat, he’s the one lawmaker standing in the way in which of an all-Republican congressional delegation in West Virginia, a state that former President Donald J. Trump carried by almost 40 factors final yr. And he’s an unlikely majority-maker of the Democratic Senate.

“We actually are the large tent,” mentioned Senator Debbie Stabenow of Michigan, earlier than knowingly including: “Now it’s a whole lot of work when you’ve an enormous tent, proper? However that’s the way in which we now have a majority.”

Whereas out of step together with his nationwide celebration on some points, and written off by components of the left as little higher than a Republican, his politics are extra advanced, even confounding, than they seem at first look.

He supplied the deciding vote on two of the most important liberal priorities of this period — blocking repeal of the Reasonably priced Care Act in 2017 and on passage of the almost $2 trillion stimulus invoice this month — whereas additionally twice voting to convict an impeached president wildly well-liked in his house state.

And whereas he could admire Mr. Byrd’s dedication to Senate custom, Mr. Manchin has not emulated his predecessor by leveraging his energy to focus relentlessly on steering spending initiatives again to West Virginia.

When Mr. Manchin was holding out on a single modification that was delaying passage of the stimulus invoice, White Home aides have been perplexed as a result of his worth for supporting the measure was not further cash for his impoverished house state. His predominant request, West Wing officers mentioned, was to pare again spending and think about Republican enter that might have made the invoice seem extra reasonable.

Mr. Manchin mentioned President Biden warned him in a cellphone name that the progressive left within the Home would possibly balk if the invoice have been considerably trimmed. “I mentioned, ‘Mr. President, all we’re attempting to do is put some guard rails on this,’” he recalled.

He was less happy about Vice President Kamala Harris’s effort to nudge him on the laws by making an look on a tv affiliate in West Virginia to advertise the invoice with out forewarning him. The clip went viral and, Mr. Manchin mentioned, prompted cleanup conversations with Mr. Biden and the White Home chief of employees, Ron Klain.

As for any strain that he could really feel on the filibuster, Mr. Manchin mentioned he had reminded Senator Chuck Schumer, the bulk chief, of how important he was to offering Democrats a majority.

He mentioned he had advised Mr. Schumer, “I do know one factor, Chuck, you wouldn’t have this downside in any respect if I wasn’t right here.”

Mr. Manchin’s resistance to eliminating the filibuster has drawn anger from many Home Democrats, significantly those that see him as successfully prioritizing bipartisanship over Black voting rights.

He’s not the one obstacle to the kind of expansive liberal agenda most popular by many congressional Democrats and even the one one nonetheless defending the filibuster. Different Senate Democrats, together with Kyrsten Sinema of Arizona, additionally share his reluctance.

But none are as keen as Mr. Manchin to revive a bygone day of collegiality. And maybe, extra to the purpose, none are as joyful as him to speak concerning the want to take action as he navigates representing a once-heavily Democratic state that had been shifting to the G.O.P. even earlier than Mr. Trump arrived on the scene.

He crossed the aisle final yr to endorse his closest Republican ally, Senator Susan Collins of Maine, and is already co-hosting bipartisan lunches together with her. He’s plotting the post-pandemic restoration of his pizza-and-beer events on the boat he calls house whereas in Washington. (It’s known as “Nearly Heaven,” the opening lyric to John Denver’s ode to West Virginia.)

Though a few of his colleagues relish the ideologically-charged prime-time cable information packages, Mr. Manchin prefers one other Washington establishment that additionally flourished in less-polarized occasions: the Sunday morning present.

Within the trend of many former governors who develop exasperated with Washington’s glacial tempo, at occasions he can barely include his impatience. He’s repeatedly mused about leaving the Senate and attempting to reclaim his outdated job in Charleston.

However those that know Mr. Manchin nicely consider he likes the eye that he receives within the capital, the identical as he did as a signal-caller in Farmington, W.V., the place he grew up close to Nick Saban, the legendary soccer coach on the College of Alabama and a lifelong buddy of Mr. Manchin.

“You’re within the sizzling seat while you’re a quarterback, but it surely’s fairly satisfying while you make progress,” mentioned Nick Casey, a Manchin ally and former chairman of the West Virginia Democratic Occasion. Mr. Casey mentioned the senator, who sustained an harm that minimize brief his enjoying days, was “the best QB who by no means acquired to begin at West Virginia College — simply ask him.”

Steve Williams, the mayor of Huntington, W.V., who served with Mr. Manchin within the state legislature, mentioned: “That is the closest he has been to how he might be as governor, really driving the agenda, pulling individuals collectively.’’

It’s the final half that almost all animates the senator. Fortunately bantering with reporters as he positions himself as a lonely, if well-covered, voice for comity, he shifts questions from coverage to course of.

“Why don’t you ask individuals when was the final time they took time to speak to a number of the individuals on this aspect?” Mr. Manchin advised a CNN reporter this week. “Attempt to persuade them, or work with them. Have you ever had dinner with them? Have you ever had a lunch with them? Have you ever had a cup of espresso with them? Attempt one thing.”

A lot of anti-filibuster Senate Democrats, although, are extra targeted on what Mr. Manchin’s help of the “speaking filibuster” may portend.

“I believe that offers us a whole lot of room for dialogue,” mentioned Senator Elizabeth Warren of Massachusetts, adopting a glass-is-half-full perspective.

What does appear clear is that Mr. Manchin isn’t going to change events.

“I don’t assume that’s going to occur, though we’d welcome him with open arms,” mentioned Ms. Collins, who has tried up to now to influence her buddy to hitch Republicans.

It’s not troublesome to see why Mr. Manchin stays in his forefathers’ celebration. A Catholic of Italian descent, he sought John F. Kennedy’s desk when he arrived within the Senate, shows an image of the slain president in his workplace foyer and may recall listening to that Massachusetts accent in his kitchen when Kennedy’s brothers got here to his dad and mom’ home throughout the West Virginia major in 1960.

“Joe jogs my memory a whole lot of the outdated conservative Democrats in Texas,” mentioned Senator John Cornyn, Republican of Texas. “They have been born Democrats. They’re going to die Democrats.”

As for the filibuster, Mr. Coons, who was sworn in alongside Mr. Manchin in 2010, mentioned liberals shouldn’t get their hopes up.

Recalling a dialog with anyone who is aware of Mr. Manchin nicely, Mr. Coons mentioned this individual advised him: “If the ghost of Robert Byrd got here again to life and mentioned the way forward for West Virginia itself is on the road he would possibly … give it some thought.”