Come January, President Barack Obama will be consigned to the sidelines as Donald Trump occupies the Oval Office and begins the work of dismantling his legacy. But there is one action that Obama could take on January 3, 2017 that could hold off some of the worst potential abuses of a Trump administration for up to a year. Obama can appoint his nominee Merrick Garland to the Supreme Court on that date, in between the two sessions of Congress.

Based on everything we know about Obama’s temperament and politics, he won’t resort to this. But given how Republicans relentlessly obstructed his efforts for eight years, he would be completely justified in playing one final trump card. And there’s a cost to ignoring that card. The fact that Democrats prefer to maintain governance norms, even while Republicans break them time and again, inescapably pushes the policymaking apparatus of the country to the right.

Here’s how it would work. Article II, Section 2 of the Constitution states, “The President shall have Power to fill up all Vacancies that may happen during the Recess of the Senate.” This has been used for Supreme Court vacancies before—William Brennan began his Court tenure with a recess appointment in 1956. Any appointments made in this fashion expire at the end of the next Senate session. So a Garland appointment on January 3 would last until December 2017, the end of the first session of the 115th Congress.

Why January 3? Because the president’s recess appointment powers were significantly constrained by a 2014 Supreme Court ruling. In a 9-0 decision in National Labor Relations Board v. Noel Canning, the Court said the president cannot appoint individuals to fill vacancies if the Senate holds “pro forma” sessions every three days. Though these sessions, common since 2011, merely gavel in and gavel out the Senate chamber, they have the practical effect of keeping the Senate active, therefore blocking the recess appointment power.

But even the Court’s most conservative members acknowledged that a president can make recess appointments during “inter-session” recesses—such as the break between the first and second year of a Congress, or the break between outgoing or incoming Congresses. There simply has to be an end point there, as a metaphysical matter. Theodore Roosevelt once used a short inter-session recess to make hundreds of appointments.