After months of pressing urgently for a deal with China, Mr. Trump abruptly shifted course in the past week, stung by what he viewed as its attempt to renege on key parts of a draft agreement. The president declared he was ready to prolong the standoff with Beijing because the cost of a trade war is much higher for the Chinese, with their huge numbers of exports to the United States, than it is for Americans.

“Talks with China continue in a very congenial manner,” Mr. Trump said Friday on Twitter. “There is absolutely no need to rush — as Tariffs are NOW being paid to the United States by China of 25% on 250 Billion Dollars worth of goods & products. These massive payments go directly to the Treasury of the U.S.”

He went even further in a subsequent tweet, claiming that tariffs would “bring in FAR MORE wealth to our Country than even a phenomenal deal of the traditional kind” — a statement that seemed to undercut his administration’s contention that China has robbed American companies of billions of dollars through coercive practices like the forced transfer of technology and unfair licensing agreements.

There is no doubt that China is being buffeted by the tariffs, which could soon apply to virtually everything it exports to the United States. Mr. Kudlow said economic growth in China would slow down as its exports diminished. He argued that the effect on the American economy would be modest — only a 0.2 percent reduction in growth — even if Mr. Trump extended tariffs across the board, as he has threatened to do.

“You got to do what you got to do,” Mr. Kudlow said. “In my judgment, the economic consequences are so small but the possible improvement in trade, and exports, and open market for the United States — this is worthwhile doing.”