For Mr. Trump, the art of this deal should be easy to grasp. To secure funding for his wall, he should offer a path to legal status or citizenship for more than 1 million “dreamers” — mainly undocumented immigrants in their teens and 20s brought to this country by their parents and raised here since childhood — a stance that is broadly popular with voters across the political spectrum. Sweeten that with continued safe harbor in the United States for some 300,000 Hondurans, Haitians and Salvadorans who have already been living here for years, legally, having been granted temporary protected status after calamities struck their home countries, and the president could lure plenty of Democrats to the table, ready to discuss his border wall.

Granted, funding the wall, even in stages, is distasteful to lots of Democrats; Rep. Nancy Pelosi (D-Calif.), the likely next House speaker, has called it “immoral.” But many in the party have supported past efforts to bolster security along the border — more Border Patrol agents, more technology and more infrastructure, including, yes, barriers.