Instead, Mr. Trump disparaged a previous version of a South Korea trade agreement as a “horror show” and a “Hillary Clinton special.” He mused to the crowd that he might hold up finalizing the deal while he pursues planned talks with North Korea.

“Certainly, the rhetoric has calmed down just a little bit, would you say?” Mr. Trump asked the crowd. “We’ll see how it all turns out.”

Mr. Trump seemed to veer off script in other areas as well. At one point, he suggested that he planned to pull American troops out of Syria, where they have aided a military campaign that has recaptured the vast majority of the territory once controlled by the Islamic State, or ISIS. “We’re knocking the hell out of ISIS,” he said. “We’ll be coming out of Syria, like, very soon. Let the other people take care of it now.”

As the crowd applauded, he added: “Very soon, very soon we’re coming out. We’re going to have 100 percent of the caliphate, as they call it — sometimes referred to as ‘land’ — taking it all back quickly, quickly.”

The comment seemed in conflict with plans by his national security team to keep a small force in place. As recently as Tuesday, Defense Secretary Jim Mattis said that while American forces were no longer in “an offensive effort on the ground” and had “drawn off slightly” to avoid accidental conflict with Russian troops, they continued to play a role. “We continue the operations in Syria,” he said.

Some foreign policy specialists said a complete withdrawal of American troops from Syria would leave a dangerous void. “If we’re pulling those troops out, we’re ceding the remnants of Syria to the Russians and the Iranians and the other actors, which actually I would argue would be a big victory for Russia,” said Jamie M. Fly, a Republican scholar at the German Marshall Fund of the United States.

Mr. Trump eventually focused on infrastructure on Thursday, zeroing in on his plan to speed up permitting. But the subject and timing of the president’s focus on his plan, announced in February, are curious. Congressional Republicans have not shown much appetite for taking up the infrastructure package, and neither have Democrats, who prefer proposals with much more federal spending.