The president can’t provide them citizenship without action by Congress. But using the same theory of “deferred action” that he employed in 2012 for children brought to the U.S. illegally by their parents, he could apply prosecutorial discretion to allow some groups of the undocumented (such as adults here illegally with children who are U.S. citizens) to obtain work permits and function openly. Though the administration is still debating the reach of Obama’s authority, some top immigration advocates hope he could legalize up to half of the undocumented population.

Such a move would infuriate Republicans, both because the border crisis has deepened their conviction that any move toward legalization inspires more illegal migration and because the president would be bypassing Congress. They would likely challenge an Obama order through both legislation and litigation. Every 2016 GOP presidential contender could feel compelled to promise to repeal the order.

Those would be momentous choices for a party already struggling to attract Hispanics and Asian-Americans. Alfonso Aguilar, executive director of the Latino Partnership initiative at the conservative American Principles Project, warns that if Republicans “again fall for the trap” and try to overturn an Obama legalization plan without offering an alternative path to legal status, the party will condemn itself to another lopsided deficit among Hispanics—and to a likely defeat—in 2016. David Ayon, senior adviser to the polling firm Latino Decisions, says that if Republicans erupt against an Obama legalization initiative, it “could turn the Latino vote as ruggedly anti-Republican as the black vote.”