Opponents of immigration reform howled that Rubio’s implied threat was a form of blackmail. But that’s exactly how reformers see the executive-order possibility -- as the potential penalty if Congress does nothing. And as the legislation’s congressional prospects get ever dimmer, the buzz about Plan B gets louder. "Some people feel like we need to cut our losses, legalize as many people as we can," Juanita Molina of Humane Borders recently told National Journal.

Richard Morales, director of deportation prevention for the PICO National Network, confirmed that activists are prepared to turn their sights on the White House. “Organizers think long term, so they know that legislation is one way, but that DACA” -- the June 2012 Deferred Action for Childhood Arrivals program -- “has proven that the administration can provide another way,” he told me in an email. The faith-based network’s “targeted deportation actions” highlighting the plight of individuals have already gotten five undocumented immigrants released from detention or spared deportation.

The Washington Post’s Brad Plumer recently examined the potential mechanics of a broad executive action halting deportations. A large number of legal experts endorsed DACA, though some conservatives argue it was unconstitutional. Depending on the extent of a broader action, a similar rationale -- assigning certain cases lower-priority status based on prosecutorial discretion -- could apply, but it would only give the undocumented a temporary reprieve and the ability to work legally, not permanent residency or citizenship.

Advocates say DACA proved that executive action to halt deportations is both legal and politically beneficial. Prior to Obama’s June 2012 announcement, his advisers knew he needed to rally a Latino community that largely felt he’d failed to keep his word to them and resented his administration’s record pace of deportations. But the Obama camp worried about a backlash from independent voters. Such a backlash never materialized; meanwhile, Hispanic voters turned out for Obama in record numbers.

Republicans who favor immigration reform have argued that their party needs to back reform to compete for the fast-growing Hispanic vote and become more viable nationally. But even those who agree with that analysis and back reform on policy grounds -- such as, by all indications, House Speaker John Boehner -- see little upside in forcing a politically difficult vote, and little downside in letting reform die a slow death. Republican Rep. Bob Goodlatte, the chairman of the Judiciary Committee, heightened reformers' fears of inaction at a recent town hall, saying, "Even if [reform legislation] doesn't go all the way through to be signed by this president ... it doesn't mean we shouldn't at least show the American people that we are interested in solving this very serious problem that we have in our country." The threat of executive action would create a disincentive for such inaction, reformers say. If Republicans refuse to act, Obama can take action -- and get all the credit from a grateful Hispanic community -- without them.