ST. LOUIS — Amid all the turmoil and uncertainty, with his White House seemingly fraying, his legislative agenda stalled and his electoral base in danger, President Trump these days finds one area of comfort: talking about his tax cuts. He finds it so reassuring, in fact, that he is increasingly talking about doing it all over again.

Mr. Trump came here to red-state Middle America on Wednesday to promote the economic benefits of the $1.5 trillion in tax breaks he signed in December, surrounding himself with workers and business owners who celebrated the prospect of more money in their pockets. As he basked in the praise, the president promised that he was not done.

“We’re now going for a Phase 2,” he told a selected group of supporters at a Boeing factory in St. Louis. He did not describe what would be in such a Phase 2 but said he would team up with Representative Kevin Brady, Republican of Texas and chairman of the House Ways and Means Committee. “It’s going to be something very special. Kevin Brady’s working on it with me.”

Mr. Brady said earlier in the day that he hoped to pass another tax-cutting bill by the end of the year. “We’re really encouraged,” he said on Fox Business Network. “Main Street optimism is at record levels. Our economy is really gaining momentum and booming in a big way. But look, we think even more can be done. We want to make sure that we’re encouraging innovation in America. We want to help families save for the long term.”