Demonstrators with the pro-immigration organization 'United We Dream' block an Washington intersection on June 5 to protest President Obama's decision to delay his revisions of deportation policies. (Marlon Correa/The Washington Post)

The two-year attempt to push immigration reform through Congress is effectively dead and unlikely to be revived until after President Obama leaves office, numerous lawmakers and advocates on both sides of the issue said this week.

The slow collapse of new border legislation — which has unraveled in recent months amid persistent opposition from House Republicans — marks the end of an effort that Democrats and Republicans have characterized as central to the future of their parties. The failure also leaves about 12 million illegal immigrants in continued limbo over their status and is certain to increase political pressure on Obama from the left to act on his own.

Some of the most vocal proponents of a legislative overhaul say they have surrendered any last hope that the parties can reach a deal. The realization marks a low point for advocates who mounted the first serious immigration push since 2007, when the Senate defeated a bipartisan effort under then-President George W. Bush.

Obama called immigration reform his top priority for his second term, and many GOP leaders suggested after the president’s reelection in 2012 that a deal was necessary for the party to broaden its appeal to Latinos.

But after a year of cajoling, prodding and berating House Republicans, leading advocates acknowledge that time has run out. Friday marks a year since the Senate approved a comprehensive immigration bill on a bipartisan vote, with no progress evident in the GOP-controlled House and few working days left in the year to approve legislation.

“Nothing’s going to happen,” Rep. Luis V. Gutierrez (D-Ill.) said in an interview after denouncing his GOP colleagues as inactive in a fiery House floor speech this week. “My point of view is, this is over. . . . Every day, they become not recalcitrant, but even more energetically opposed to working with us. How many times does someone have to say no until you understand they mean no?”

Chances of legislation advancing in the House are “next to zero,” said Sen. Jeff Flake (R-Ariz.), a member of a bipartisan group of eight senators who led reform efforts in the chamber.

“It’s a shame,” he added. But after talking to GOP colleagues in the House, “there’s just no appetite for it right now.”

Hopes for a broad immigration deal already had dimmed considerably by this spring. But the Obama administration and its Democratic allies believed, based on signals from House Speaker John A. Boehner (Ohio) and other GOP leaders, that there was a final window for possible agreement this summer before the midterm elections.

Two recent developments, however, doomed whatever chances remained, advocates and lawmakers said. House Majority Leader Eric Cantor (R-Va.) lost a primary election this month to a tea-party-backed challenger who ran on a strong anti-immigration platform. In addition, a new crisis erupted on the Mexican border, as tens of thousands of unaccompanied Central American children were apprehended crossing illegally into Texas over the past several months.

House Republicans have cited both situations as evidence that the time is not right for a bipartisan deal that would provide legal status, and potentially citizenship, to millions of illegal immigrants. Many also have stepped up their rhetoric on the issue, blaming the administration for the border crisis and saying Obama has not convinced them that he will adequately enforce immigration laws.

Several House Republicans suggested at a hearing this week that the United States should, among other things, cut off all economic aid to Mexico until the border is secure, build hundreds of miles of new fencing to help prevent more illegal immigration and immediately put the children arrested by Border Patrol officers on buses back to their home countries.

“I think what you need to do is ask the Guatemala government where they want these kids dropped off when the buses bring them back down there,” Rep. Mike D. Rogers (R-Ala.) told Homeland Security Secretary Jeh Johnson at the hearing.

In addition to considering Obama’s border policies lax, Republicans also object to his 2012 decision not to deport young immigrants who were brought to the country illegally by their parents. Boehner said this week that House Republicans intend to sue the president over his use of such executive powers.

“If the administration were serious about enforcing the law, they would not take the law into their own hands and repeatedly find ways to not enforce the law,” House Judiciary Committee Chairman Bob Goodlatte (R-Va.) told reporters at a Christian Science Monitor breakfast Thursday.

Asked later about the prospects for immigration reform this year, Goodlatte said, “The environment for doing this is exceedingly difficult.”

White House officials acknowledged this week that they have seen no signs of movement on immigration from House Republicans in recent weeks. The president is likely to face a shift in tactics among immigrant advocates, who will renew demands that he use his executive powers to further stem deportations.

Obama rebuffed such calls from Democrats and advocacy groups in the spring, asking that they present a united front against House Republicans through the end of July, which he described as the final window of time for a potential breakthrough. He delayed an internal review of deportation policies at the Department of Homeland Security until after the summer.

Asked this week whether House Republicans had responded to that opportunity, White House press secretary Josh Earnest said, “Sadly, no.”

“Unfortunately, right now I think the early indications are not very good for a lot of progress on this front,” he said. “For a year, there has been a very clear template . . . but House Republicans at every turn have blocked any sort of progress.”

Frank Sharry, executive director of America’s Voice, a leading immigrant rights group, predicted that pressure on Obama would “increase significantly in July” because advocates have lost hope in the legislative process.

Boehner has named a working group of seven GOP members to monitor the administration’s response to the border crisis involving unaccompanied children. He said the group will report back to him after the Fourth of July holiday recess with suggestions for potential changes in the law.

But even if Boehner were to revive House efforts to pursue legislation, the calendar leaves precious little time.

The House is in session for four weeks until the five-week summer recess that starts in early August. After that, there are just 10 legislative days in September — probably devoted to a host of complex fiscal issues, including a new highway bill and a measure to keep the federal government open when the new fiscal year begins Oct. 1. The House has two legislative days scheduled in October, but those sessions could be canceled to allow members to spend more time at home campaigning for the midterm elections.

The potential of an electoral upheaval leaves the lame-duck session after the midterms fraught with uncertainty. Members of both parties suggest that it is highly unlikely that immigration reform could be restarted next year, when the early stages of the 2016 presidential campaign takes shape.

Democrats have signaled that they will continue pushing Republicans to act. Senate Majority Leader Harry M. Reid (Nev.), House Minority Leader Nancy Pelosi (Calif.) and other Democrats rallied Thursday morning to once again make their case, repeating justifications for the legislation that they have used repeatedly for the past two years.

At a breakfast Wednesday held by the Wall Street Journal, Sens. Charles E. Schumer (D-N.Y.) and John McCain (R-Ariz.) — two sponsors of the Senate immigration bill — acknowledged that the chances of House legislation are exceedingly slim.

“I can’t tell you we have a great shot at it,” said McCain, who was his party’s 2008 presidential nominee. “But I know the consequences of failure.”