“They do not want Donald Trump’s populist, economic nationalist agenda to be implemented,” Mr. Bannon said. “It’s obvious as night follows day.” He cited as an example a request that Mr. McConnell once made of Mr. Trump to stop talking about “draining the swamp.”

Mr. Bannon predicted deep division within the Republican Party over Mr. Trump’s recent move to end the program that provided temporary relief from deportation for hundreds of thousands of young people in the United States illegally. The president set a March end date for the program and asked Congress to come up with a solution in the meantime, a task that Mr. Bannon said could split Republicans and cost them their House majority in the 2018 midterm elections.

“If this goes all the way down to its logical conclusion, in February and March it will be a civil war inside the Republican Party,” he said.

When Mr. Rose asked whether Mr. Bannon’s opposition to the immigration program was true to his Catholic faith, Mr. Bannon took aim at church leaders and claimed they relied on illegal immigration to fill pews. “The bishops have been terrible about this,” he said. “You know why? Because unable to really to come to grips with the problems in the church, they need illegal aliens. They need illegal aliens to fill the churches.”

Cardinal Timothy M. Dolan, the archbishop of New York, called Mr. Bannon’s comments “preposterous and rather insulting.”

In the interview from his Washington home, Mr. Bannon reacted defensively when asked whether his clout in the White House had diminished by the time he left. “I had the same influence on the president I had on Day 1,” he said.