After four years in office, President Barack Obama has failed to reach a deal on immigration – and that has left the president looking for a big summertime achievement.

Obama is still in search of a marquee legislative accomplishment to mark his second four years. And now that there is growing uncertainly over a sweeping immigration overhaul measure, he seems to be reaching for another legislative breakthrough.

His advisers now concede that their best shot at changing the immigration system might come in the fall, after lawmakers return from their August recess. But that could be a long shot during a period already crowded with other issues.

During the autumn months, Obama's administration will be dealing with one of the most challenging aspects of the historic health care overhaul — signing up millions of Americans for insurance coverage. And if that's not enough, Obama also will be locked in an unexpected battle over domestic food aid — while working through budget disputes with Congress as the new fiscal year looms in October and the government approaches its borrowing limit. Then there's overseas turmoil in Egypt and Syria.

"He has a Herculean task ahead of him," Rep. Emanuel Cleaver, the past chairman of the Congressional Black Caucus, said hours after he and other black lawmakers met with the president this week. "I am convinced he is fully aware of the difficulties in his path, difficulties that could reduce his legacy."

Before his re-election, Obama liked to tell supporters that a second term would "break the fever" with Republicans, arguing that they no longer would need to routinely block his agenda because he wouldn't be seeking election again. By last month, that optimism was gone.

"When it comes to doing the things that need to get done, we're just not getting a lot of cooperation from the other side," he grumbled to donors at a June fundraiser in Palo Alto, Calif.

Republicans maintain that Obama's initiatives simply go further than they are willing to go. On immigration, many oppose a path to citizenship for immigrants illegally in the United States — a key provision in the overhaul Obama seeks.

"No one expected that postelection everything would be easy, that all the historic, huge differences between the parties on the big issues would all go away," said senior Obama adviser Dan Pfeiffer.

On immigration, he says that "there are some serious challenges in the way, but six months in and having a bill through the Senate with a bipartisan majority is historically rapid progress."

Still, White House aides had argued that a solid bipartisan vote on immigration in the Senate would give the legislation momentum through the House. Two weeks ago, at a news conference in South Africa, Obama called on the House to act before the August recess. "Now is the time," he declared.

House Republicans ignored him, saying they would not take up the Senate bill and would instead tackle immigration in a piecemeal way. "I'm much more concerned about doing it right than I am in meeting some deadline," House Speaker John Boehner said.

That decision put a sizable question mark over one of Obama's biggest second-term priorities.

"This is going to be a tougher fight than people had anticipated," said Simon Rosenberg, president of NDN, a Democratic-leaning Washington think tank and a longtime advocate of overhauling immigration laws. "It could go on for six months; it could go on for the next couple of years."

Some Obama allies fear that failure to win on immigration — an issue many believed was ripe for change after last year's elections — will simply embolden his opponents. Cleaver, a Missouri Democrat, said it "could conceivably wound the president in a way that would make the next three years move very, very slowly and painfully."

Others are still upbeat.

"It's an important moment that could help him if something gets done, if not in his timeline, in the near future," said Patrick Griffin, who handled legislative relations for former President Bill Clinton.

As significant as the immigration legislation may be, Obama is treading carefully, wary of alienating Republicans. He has faced some pressure to speak out more forcefully and to use the power of his office to give immigration the visibility he has given to past clashes with Congress over taxes and student loans.

"Every situation is different," David Plouffe, Obama's former top political adviser, said after visiting the White House this week. "Some have called for more of an approach that is geared to the outside. I think you have to wait and see how this develops."

While White House aides and advisers believe Republicans will inflict long-lasting political damage on their own party if they continue to block a comprehensive immigration bill, those advisers say Obama is not ready to hit the road and wage a full-throated partisan fight.

"We're doing meetings, we're talking to folks, we're behind the scenes at every step," Pfeiffer said. Asked when the pressure might mount, he said: "There might be a moment where the hammer comes out. But we're not there yet."

Based on reporting by The Associated Press.

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