“This is going to be a bumpy ride,” Mr. Bannon said in an interview Monday. “I don’t think he’ll back off because of a couple of bad days in the stock market — and I do think he’ll have a couple of bad days.”

But Mr. Bannon said he worried about the lack of support for Mr. Trump’s moves within the Republican establishment and about pressure from major party donors like Sheldon G. Adelson, the Las Vegas casino magnate who has huge investments in the Chinese territory of Macao.

“The donor class and the politicians, from Paul Ryan to Mitch McConnell, have thrown in completely with the ‘we don’t want a trade war’ crowd,” he said. “My fear is ‘What does the money want to do?’”