However, President Obama can still act to bring humanity and justice to an immigration system notoriously lacking in both. He can do so by using the power the Constitution grants him — and only him — to pardon individuals for “offenses against the United States.”

The debate over the deportation deferral program has been framed as a question of the division of powers. Both sides agree that Congress is the only entity that gets to define offenses against the United States. Reasonable commentators also agree that the president enjoys prosecutorial discretion to determine which deportation cases to pursue and which to forgo. The difficult question is whether a categorical decision to decline to prosecute millions begins to intrude on Congress’ power. While the program is consistent with the way previous presidents have used prosecutorial discretion, without guidance from the Supreme Court, debate will surely continue.

There is one area, however, where the president’s unilateral ability to forgo punishment is uncontested and supported by over a hundred years of Supreme Court precedent: the pardon power. It has been consistently interpreted to include the power to grant broad amnesties from prosecution to large groups when the president deems it in the public interest.

Such pardons have been used by presidents including George Washington, Thomas Jefferson, James Madison, Abraham Lincoln and Andrew Johnson. Most recently, Jimmy Carter issued a pardon to around half a million men who had violated draft laws to avoid military service in Vietnam.

It’s a common assumption that pardons can be used only for criminal offenses, and it’s true that they have not been used before for civil immigration violations. However, the Constitution extends the power to all “offenses against the United States,” which can be interpreted more broadly than just criminal offenses.

A pardon could not achieve everything the deferred deportation program aspired to — notably, it could not deliver work permits. However, it has a certain operational elegance to it that would avoid many of the political battles surrounding the deferral program. No application process would be necessary. A pardon becomes immediately effective upon issuance by a president. With fewer than 300 words and a signature, President Carter’s pardon became effective on his first full day in office.

The enormous administrative undertaking that would be required to put into effect the deferred deportation program — which some in Congress had hoped to defund — would thus be wholly unnecessary. Indeed, Congress would be impotent to restrict the president’s pardon as the Supreme Court has made clear that “Congress cannot interfere in any way with the president’s power to pardon.” If immigration enforcement agencies or any future administration failed to respect the pardon, individual beneficiaries could use it as a shield in any deportation proceedings that followed.

President Obama has plenty of time left to issue such a pardon. There is solid historical and legal precedent for him to do so. And although it would probably bring about legal challenges, opponents could not use the legal system to simply run out the clock, as they have with his deferred deportation program. A deferred deportation program could be undone by a President Trump. Unconditional pardons, in contrast, are irrevocable.

Finally, some would surely argue that a pardon protecting a large category of immigrants from deportation would, just like the deportation deferral program, effectively amount to a repeal of laws enacted by Congress. However, pardons do nothing to alter the law. They protect certain past offenders from punishment and prosecution, but leave the law unchanged as applied to any future violators.

President Obama has deported around 2.5 million people. That is about the same number as were deported in the entire 20th century. His apparent strategy was to demonstrate his bona fides on enforcement in order to persuade recalcitrant Republicans to work with him on immigration reform. It didn’t work. It turns out that you don’t convince people to be more humane on immigration by deporting immigrants hand over fist.

We are left with a brutal legacy of millions of families torn apart, many simply for doing what they needed to do to protect and feed their children. President Obama will not be judged on his intentions or his attempts on immigration, but rather on his real impact. This is his last chance to establish a legacy of pragmatic compassion.