WASHINGTON — Within the nationwide battle over voting rights, Democrats have rested their hopes for turning again a wave of new restrictions in Republican-led states and increasing poll entry on their slender majorities in Congress. Failure, they’ve repeatedly insisted, “shouldn’t be an possibility.”

However as Republican efforts to clamp down on voting prevail throughout the nation, the drive to enact essentially the most sweeping elections overhaul in generations is faltering within the Senate. With a self-imposed Labor Day deadline for motion, Democrats are struggling to unite round a technique to beat stable Republican opposition and an almost certain filibuster.

Republicans in Congress have dug in in opposition to the measure, with even essentially the most average dismissing it as bloated and overly prescriptive. That leaves Democrats no possibility for passing it aside from to attempt to power the invoice via by destroying the filibuster rule — which requires 60 votes to place apart any senator’s objection — to move it on a easy majority, party-line vote.

However Senator Joe Manchin III of West Virginia, the Democrats’ decisive swing vote, has repeatedly pledged to protect the filibuster and is refusing to signal on to the voting rights bill. He calls the laws “too darn broad” and too partisan, regardless of endorsing such proposals in previous classes. Different Democrats additionally stay uneasy about a few of its core provisions.

Navigating the 800-page For the Individuals Act, or Senate Invoice 1, via an evenly break up chamber was by no means going to be a simple process, even after it passed the House with only Democratic votes. However the Democrats’ technique for transferring the measure more and more hinges on the longest of lengthy photographs: persuading Mr. Manchin and the opposite 49 Democrats to assist each the invoice and the gutting of the filibuster.

“We ought to have the ability to move it — it actually could be transformative,” Senator Chris Coons, Democrat of Delaware, mentioned just lately. “But when we’ve a number of members of our caucus who’ve simply point-blank mentioned, ‘I cannot break the filibuster,’ then what are we even doing?”

Summarizing the get together’s problem, one other Democratic senator who requested to stay nameless to debate technique summed it up this fashion: The trail to passage is as slender as it’s rocky, however Democrats don’t have any alternative however to die making an attempt to get throughout.

The hand-wringing is more likely to solely intensify within the coming weeks. Senator Chuck Schumer of New York, the bulk chief, vowed to power a flooring debate in late June, testing Mr. Manchin’s opposition and laying the groundwork to justify scrapping the filibuster rule.

“Hopefully, we will get bipartisan assist,” Mr. Schumer mentioned. “To date, we’ve not seen any glimmers on S. 1, and if not, every thing is on the desk.”

The stakes, each politically and for the nation’s election techniques, are monumental.

The invoice’s failure would enable the enactment of restrictive new voting measures in Republican-led states similar to Georgia, Florida and Montana to take impact with out legislative problem. Democrats worry that may empower the Republican Occasion to pursue a technique of marginalizing Black and younger voters based mostly on former President Donald J. Trump’s false claims of election fraud.

If the measure handed, Democrats might successfully overpower the states by setting up new nationwide mandates that they arrange automated voter registration, maintain common no-excuse early and mail-in voting, and restore the franchise to felons who’ve served their phrases. The laws would additionally finish partisan gerrymandering of congressional districts, restructure the Federal Election Fee and require tremendous PACs to reveal their large donors.

A legion of advocacy teams and civil rights veterans argue that the struggle is simply beginning.

“This sport isn’t executed — we’re simply gearing up for a flooring struggle,” mentioned Tiffany Muller, the president of Finish Residents United and Let America Vote, that are spending millions of dollars on television ads in states like West Virginia. “On the finish of the day, each single senator goes to have to select if they will vote to uphold the suitable to vote or uphold an arcane Senate rule. That’s the state of affairs that creates the stress to behave.”

Proponents of the overhaul on and off Capitol Hill have targeted their consideration for weeks on Mr. Manchin, a centrist who has expressed deep issues concerning the penalties of pushing via voting laws with the assist of just one get together. To date, they’ve taken a intentionally hands-off strategy, betting that the senator will understand that there isn’t any actual compromise available with Republicans.

There’s little signal that he has come to that conclusion on his personal. Democrats huddled final week in a big convention room atop a Senate workplace constructing to debate the invoice, ensuring Mr. Manchin was there for an elaborate presentation about why it was important. Mr. Schumer invited Marc E. Elias, the well-known Democratic election lawyer, to elucidate intimately the extent of the restrictions being pushed via Republican statehouses across the nation. Senators as ideologically numerous as Raphael Warnock of Georgia, a progressive, and Jon Tester of Montana, a centrist, warned what may occur if the get together didn’t act.

Mr. Manchin listened silently and emerged saying his place had not modified.

“I’m studying,” he informed reporters. “Mainly, we’re going to be speaking and negotiating, speaking and negotiating, and speaking and negotiating.”

Regardless of the extraordinary concentrate on him, Mr. Manchin shouldn’t be the one hurdle. Senator Kyrsten Sinema, Democrat of Arizona, is a co-sponsor of the election overhaul, however she has additionally pledged to not change the filibuster. A handful of different Democrats have shied away from definitive statements however are not any much less desperate to cast off the rule.

“I’m to not that time but,” Mr. Tester mentioned. He additionally signaled he is likely to be extra comfy modifying the invoice, saying he “wouldn’t lose any sleep” if Democrats dropped a provision that may create a brand new public marketing campaign financing system for congressional candidates. Republicans have pilloried it.

“To begin with, we’ve to determine if we’ve all of the Democrats on board. Then we’ve to determine if we’ve any Republicans on board,” Mr. Tester mentioned. “Then we will reply that query.”

Republicans are hoping that by banding collectively, they’ll doom the measure’s prospects. They succeeded in deadlocking a key committee considering the legislation, although their opposition didn’t bar it from advancing to the complete Senate. They accuse Democrats of utilizing the voting rights provisions to distract from different provisions within the invoice, which they argue are designed to present Democrats lasting political benefits. If they’ll forestall Mr. Manchin and others from altering their minds on retaining the filibuster, they may have thwarted the complete endeavor.

“I don’t assume they’ll persuade 50 of their members that is the suitable factor to do,” mentioned Senator Roy Blunt, Republican of Missouri. “I believe it might be exhausting to elucidate giving authorities cash to politicians, the partisan F.E.C.”

Within the meantime, Mr. Manchin is pushing the get together to embrace what he sees as a extra palatable various: laws named after Consultant John Lewis of Georgia, the civil rights icon who died last year, that may restore a key provision of the Voting Rights Act of 1965 that the Supreme Court docket struck down in 2013.

That measure would revive a mandate that states and localities with patterns of discrimination clear election legislation modifications with the federal authorities prematurely, a requirement Mr. Manchin has advised must be utilized nationwide.

The senator has mentioned he prefers the strategy as a result of it might restore a observe that was the legislation of the land for many years and loved broad bipartisan assist of the type essential to make sure the general public’s belief in election legislation.

In actuality, although, that invoice has no higher probability of turning into legislation with out eliminating the filibuster. For the reason that 2013 resolution, when the justices requested Congress to ship them an up to date pre-clearance formulation for reinstatement, Republicans have proven little curiosity in doing so.

Just one, Senator Lisa Murkowski of Alaska, helps laws reinstating the voting rights provision within the Senate. Requested just lately concerning the prospect of constructing extra Republican assist, Ms. Murkowski identified that she had been unable to draw one other co-sponsor from her get together within the six years because the invoice was first launched.

Complicating issues, it has but to really be reintroduced this time period and is probably not for months. As a result of any new enforcement provision must move muster with the courts, Democrats are continuing cautiously with a sequence of public hearings.

All that has created an infinite time crunch. Election legal professionals have suggested Democrats that they’ve till Labor Day to make modifications for the 2022 elections. Past that, they may simply lose management of the Home and Senate.

“The time clock for that is working out as we strategy a midterm election once we face dropping the Senate and even the Home,” mentioned Consultant Terri A. Sewell, a Democrat who represents the so-called Civil Rights Belt of Alabama and is the lead sponsor of the invoice named for Mr. Lewis.

“If the vote and defending the rights of all People to train that the majority valuable proper isn’t value overcoming a procedural filibuster,” she mentioned, “then what’s?”

Luke Broadwater contributed reporting.