A leading Latino Republican is warning that if the GOP-controlled House does not move on immigration reform by the August recess, Obama will employ executive action to ease deportations on his own — making any legislative reform politically impossible until at least 2017.

That would mean that if Republicans don’t act on reform by August, they may lose their chance to place their stamp on reform — and begin to repair their Latino problem — before the next presidential election.

“I’m convinced that if we don’t get it done by the August break, the president, who is feeling a lot of pressure from having not done anything on immigration reform, will feel that he has to act through executive action,” GOP Rep. Mario Diaz-Balart of Florida, a leading Republican player on immigration, told me today.

“If he does that, the window for Republicans and Democrats to negotiate on this issue is closed until the next president,” Diaz-Balart continued.

Diaz-Balart took pains to stress he does not think reform is dead for the year. He reiterated what he told me recently, that he has legislative language ready to go on a form of legal status for the 11 million that he believes could win substantial Republican and Democratic support, and said he continues to talk to lawmakers on both sides of the aisle. John Boehner has shelved reform, but most people closely following the debate think there’s still an outside shot — a very long one, to be sure – that GOP leaders might decide to allow proposals to move forward after the primaries are over, and before recess.

Some have suggested that acting this year is politically risky for Republicans because it could depress the base in advance of the 2014 election — and that Republicans can simply act in 2015. But Diaz-Balart dismissed that idea, noting that GOP presidential primary politics would be underway. “Then it’s a presidential election cycle and its all politics all the time,” he said.

Some Republicans appear to believe that if Obama does act unilaterally, it would be a political gift to them, allowing them to avoid blame for inaction on reform by arguing they were right all along that the president can’t be trusted to enforce the law. But Diaz-Balart offered an alternate view, suggesting failure by Congress to act could give Obama cover to move forward alone.

“It would give every excuse for the president to move forward on dealing with the undocumented while blaming Republicans for Congress’ inaction,” Diaz-Balart said.

One key question is whether House Republicans see the prospect of executive action by Obama as a deadline of sorts for them, which is the implication of Diaz-Balart’s view of the timeline. One House GOP leadership aide recently told me that GOP leaders take the possibility of Obama acting alone seriously, and while they acknowledge that acting legislatively next year could also be very hard, the prospect of unilateral action doesn’t change their calculus on whether they’ll act this year. That calculus turns heavily on the politics inside the House GOP caucus.

If Diaz-Balart is right, Obama will have to act if House Republicans don’t, and as the chatter about executive action grows louder in coming weeks, it’ll be interesting to track reactions among them. A few will probably react along the lines of Diaz-Balart — arguing Republicans should act before their chance to place their stamp on reform slips away – which will indicate that they actually want reform to happen. Others will probably seize on it as an excuse to harden opposition — as more proof you can’t trust Obama. If that latter argument gains steam, it will be yet another sign that legislative reform just isn’t going to happen, which would in turn mean Republicans are very likely heading into another presidential election with their Latino problem unaddressed.

Greg Sargent writes The Plum Line blog, a reported opinion blog with a liberal slant -- what you might call “opinionated reporting” from the left.