WASHINGTON — President Trump cast his trade accord with President Xi Jinping of China as a huge victory for American farmers, automakers and other key political constituencies — statements that helped send volatile financial markets higher on Monday and seemed intended to calm worries about the economic toll of a protracted trade war.
Yet 48 hours after the deal was struck, several big areas of contention remained unresolved and Mr. Trump appointed a veteran trade negotiator with deep skepticism toward China to lead the talks for the United States.
Mr. Trump’s choice of Robert Lighthizer, the United States trade representative, to lead the negotiations is significant, given that the official statements from Saturday’s meeting included only vague commitments and that deep divisions remain, particularly over China’s treatment of American companies and push to obtain trade secrets and intellectual property.
The administration has been intensely conflicted about how to approach China, with hard-liners like Mr. Lighthizer advising Mr. Trump to use punishing tariffs to force Beijing to change, and more moderate advisers, like Steven Mnuchin, the Treasury secretary, encouraging the president to avoid a trade war.
Mr. Lighthizer, who recently brokered the new North American trade deal, is a longtime critic of China’s trade practices and has repeatedly cautioned Mr. Trump not to accept vague promises that fail to materialize. He will be taking the reins from Mr. Mnuchin, who led previous rounds of negotiations with the Chinese but could not close a deal that satisfied the president.
That choice could rattle the Chinese, who have cozied up to Mr. Mnuchin, viewing him as more moderate.