2. Sixteen states have banded together to challenge President Trump’s declaration of a national emergency at the border, setting up a constitutional clash over the scope of presidential emergency powers.

Their lawsuit argues that the president doesn’t have the power to divert federal funds to build his promised border wall because Congress controls spending. House Democrats are also gearing up to confront the president. Above, workers reinforcing a section of the border fence near Tijuana, Mexico.

Our limited-run weekly newsletter, Crossing the Border, offers a deeper understanding of an issue that seems to have taken over the U.S. political agenda.