Donald J. Trump may be known for his combative, vindictive style. But as a candidate for president in 2024, he cast himself as a man of peace. His toughness and the “respect” he enjoys from foreign leaders, he insisted, would enable him to settle conflicts almost with a snap of his fingers.

“My proudest legacy will be that of a peacemaker and unifier,” Mr. Trump said in his January inaugural address.

The war in Ukraine could be ended in as little as 24 hours, he said. He would knock heads to reach an agreement between Israel and Hamas to stop the fighting in Gaza.

And he said he would strike a nuclear deal with Iran, “because the consequences are impossible. We have to make a deal.”

A day after Israel began a massive attack on Iran, however, Mr. Trump’s peace projects are in tatters. The fighting in Ukraine rages on and Mr. Trump appears to have lost patience with efforts to end that war. In Gaza, both Israel and Hamas cling to basic positions they staked out long before Mr. Trump took office.

And instead of announcing a new nuclear deal with Tehran, a president who often denounces America’s history of “stupid” Middle East wars is trying to navigate a dangerous conflict between Iran and Israel, the closest U.S. partner in the region.