For the last three years, a previously obscure emergency public health order allowed politicians to temporarily sidestep one of the most complicated issues in American politics — migration at the United States' southern border. Former President Donald Trump invoked Title 42 in the spring of 2020 as COVID-19 cases were spreading. And that meant that border agents could quickly process and expel migrants. But as COVID cases dipped, the rule remained in place, allowing officials to control the flow of migrants.

At 11:59 pm last Thursday, the policy expired.

Now, the old order is back, and officials must either detain migrants who cross into the U.S. or release them. There was no immediate chaotic rush of migrants at the border, as some had anticipated. But a lot of uncertainty remains about what will transpire in the months to come — both procedurally and politically.

And there is a lot at stake for President Biden himself. He has to figure out how to navigate asylum law and avoid a humanitarian crisis, all while gearing up for a reelection bid in which he's facing political pressure from the left flank of his own party and Republican critics on the other side.