With immigration reform dead on Capitol Hill, President Obama says he will use his executive authority to make changes to the law himself. “I’m beginning a new effort to fix as much of our immigration system as I can on my own,” Obama said in June. “If Congress will not do their job, at least we can do ours.”

How much can he do without congressional approval? Actually, quite a bit. The president has the power to grant many of the estimated 11 million undocumented immigrants already in the U.S. relief from deportation simply by instructing the Department of Homeland Security not to pursue their cases. In 2012, after Congress repeatedly declined to pass the Dream Act, which would have offered citizenship to immigrants whose parents brought them to the U.S. illegally as children, Obama said he would offer the immigrants “deferred action”—essentially a two-year stay on deportation proceedings. More than 550,000 people have qualified.

The National Council of La Raza, a Hispanic civil rights group, the AFL-CIO, and other immigrant advocates have urged the White House to extend deferred action—which can include authorization to work in the U.S.—to anyone who would have qualified for the “pathway to citizenship” under the terms of the immigration reform bill passed by the Senate last year. That program would have covered people who’ve been in the U.S. since 2011 and don’t have serious criminal records, which accounts for about two-thirds of all undocumented immigrants. “These are people that we know are going to eventually be legalized by Congress,” says Marshall Fitz, director of immigration policy for the liberal Center for American Progress, who adds that polls show a majority of Americans support the Senate bill.

What Obama can’t do is declare an amnesty. “The president cannot give people green cards—you know, lawful permanent resident status,” says Hiroshi Motomura, a UCLA law professor. “This is all temporary reprieve.” The president can make changes to the way immigration laws are enforced. Liberal groups are pressing for an end to federal immigration enforcement programs like Secure Communities, under which local police share the fingerprints of people they arrest with federal immigration authorities. Civil liberties advocates say such initiatives violate privacy laws and that some U.S. citizens have been mistakenly held as undocumented immigrants. Because the rules were created by Homeland Security and not Congress, “there would be no question that the president could suspend or terminate that program,” says Yale Law School professor Michael Wishnie.

Beyond these steps, the president begins to bump up against the limits of his power. Obama says he wants to redeploy federal immigration enforcement agents to the Mexican border. That’s something he can do within the confines of existing law, but he needs Congress to agree to pay for it. On July 8 the White House requested $3.7 billion in emergency appropriations for additional surveillance, detention, and services for migrants, and to hire more immigration court judges to expedite deportations, particularly of unaccompanied children arriving from Central America. House Republicans were quick to counter with threats to reject the special requests—and withhold money for federal agencies next year if the president moves ahead without their approval. “There’s always appropriations tools where you can direct and deny funding,” says Republican Representative Tom Cole of Oklahoma, a deputy majority whip. “There’s abundant weapons there.”

Obama has said he’ll announce his next steps by the end of the summer. With the midterm elections approaching and the Democrats’ Senate majority at risk, the question is how far he’s prepared to go. “As a legal matter, his discretion is really broad,” says Motomura. “As a political matter, I think it’s much more constrained.”