A tax-raising deal at the beginning of the year looked like it might be a breakthrough, signaling improved second-term relations between newly re-elected President Barack Obama and a divided Congress. At least that’s what the White House hoped.

But six months later, growing uncertainty over a sweeping immigration overhaul measure has dimmed expectations for a big summertime achievement and left Obama still in search of a marquee legislative accomplishment to mark his second four years.

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.

The president already has faced two legislative setbacks this year: a gun control measure that Republicans blocked in the Democratic-controlled Senate and the failure to avoid automatic spending cuts that further trimmed the government’s budget.

“He has a Herculean task ahead of him,” Rep. Emanuel Cleaver, the past chairman of the Congressional Black Caucus, said 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.

Many refused to support expanded background checks for firearm purchases at gun shows and online. They rejected Obama’s efforts to combine spending cuts with more tax increases. And now, on immigration, many oppose a path to citizenship for immigrants illegally in the United States — a key provision in the overhaul Obama seeks.

Another trouble spot for Obama emerged just recently on what historically has been a bipartisan issue: approval of legislation that includes money for agricultural subsidies and food stamps.

The Senate passed a single measure that included money for both, but House Republicans approved the farm bill only after stripping out the food stamp program.

Obama, who opposes proposed cuts to food stamps in the House bill, has threatened a veto, signaling the battle could consume the coming weeks.

White House aides say they’re not surprised by the difficulties Obama faces.

“No one expected that post-election 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.

“We’re six months into our term,” he added. “We’ve already fulfilled one of our biggest campaign pledges in preserving tax cuts for the middle class and having the rates of the wealthy go back to what they were under President Clinton.” 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.”