BEIJING — Xi Jinping started his second term as China’s president on Saturday, flanked by a new vice president, Wang Qishan, who even without any other titles to his name is shaping up as a potent deputy to Mr. Xi, with a potentially powerful say in grappling with the Trump administration over trade disputes.

Mr. Xi and Mr. Wang shook hands after the National People’s Congress, the Communist Party-controlled legislature, endorsed them for the posts in a closely controlled ritual ballot. Mr. Xi won all of the 2,970 votes cast for president, and all but one legislator voted for Mr. Wang, admired and feared for his previous role as the party’s chief anticorruption enforcer, for vice president.

“We all support Wang Qishan to be vice president,” Fang Jianqiao, a delegate from Zhejiang Province in eastern China, said before the vote. “His partnership with President Xi Jinping can promote better contacts abroad,” he said. “It will also help to better fight corruption and promote clean government.”

In China, the vice presidency is not an inherently powerful job. The previous incumbent, Li Yuanchao, faded from view, clouded by corruption scandals involving former subordinates and a widespread impression that Mr. Xi disdained him. But Mr. Wang appears poised to break that pattern and serve as an influential adviser and political guardian for Mr. Xi.