President Trump cut his growing political losses on Friday by agreeing to reopen the government for three weeks pending new border-spending negotiations. House Speaker Nancy Pelosi emerges as the winner in this showdown, at least in the short term. We’ll now see if she’s serious about negotiating a deal on immigration or simply wants to humiliate Mr. Trump.

The President agreed to sign the short-term funding bill without money for his border wall. He had little political choice. Most voters blamed him for the shutdown, and...