WASHINGTON — Vice President Mike Pence will signal a far tougher American line on China on Thursday, delivering a speech in which he is expected to accuse the Chinese of aggressive moves against American warships, of predatory behavior against their neighbors, and of a sophisticated influence campaign to tilt the midterms and 2020 elections against President Trump.

“To put it bluntly, President Trump’s leadership is working,” Mr. Pence is to say, according to excerpts from his speech provided on Wednesday night. “China wants a different American president.”

Mr. Trump accused China last week of meddling in the midterm elections, saying at the United Nations in New York that it was retaliating for his imposition of tariffs on $250 billion worth of Chinese goods. But the president was careful not to antagonize China’s president, Xi Jinping, with whom he has cultivated a personal relationship.

Mr. Pence, however, will broaden the attack on China to encompass its rapid military buildup in its coastal waters; its use of debt financing to corrupt financially vulnerable countries; and its influence campaign in American news media, at think tanks and on college campuses, which he will claim is more extensive than that deployed by the Russians in 2016.