Sen. John McCain (R-Ariz.) speaks with reporters outside the Senate chamber on Thursday. (Drew Angerer/Getty Images)

BRUSSELS — President Trump should listen to his national-security Cabinet officials on foreign policy matters, not chief strategist Stephen K. Bannon, Sen. John McCain (R-Ariz.) told an audience of European leaders Friday.

The chairman of the Armed Services Committee also rebuked what he called the isolationist view in U.S. foreign policy and gave some unsolicited advice to Trump, whom he has not spoken with since the election, on how to conduct world affairs going forward.

There is deep uncertainty regarding the future of U.S. foreign policy, especially where it relates to Europe, McCain told the Brussels Forum, an annual meeting of mostly American and European officials and experts. Fueling that uncertainty is a lack of clarity about where Trump is getting his foreign-policy advice. Although he has not spoken to Trump, McCain said he speaks to Trump national-security officials “almost daily,” including Defense Secretary Jim Mattis, Director of National Intelligence Dan Coats and national security adviser H.R. McMaster.

“I’m not positive who the president listens to but I am confident that if he listens to those individuals, we’ll be in pretty good shape,” McCain said. “I believe in the people around the president as far as national security is concerned. Their commitment, their sacrifice, their lifetime of service in the military and positions of responsibility gives me great confidence.”

Then McCain singled out Bannon as a potentially bad influence on the president when it comes to foreign policy.

“I know also that there are statements and sometimes — not so much policies but comments that come from the White House that clearly indicates that Mr. Bannon is the one who is having a significant impact on the president’s statements and thinking,” said McCain. “And that is a concern to me. I just have to say that honestly.”

Bannon did not respond to a request for comment. Not referring to Bannon directly, McCain criticized many of the foreign-policy positions Bannon and Trump have articulated in the past, including on trade and Russia. He also compared Trump’s slogan for foreign policy, “America First,” to its original usage by isolationist foreign-policy leaders in the 1930s.

“There’s an isolationist element that’s always been there in the United States of America,” McCain said. “You could go all the way back to the days Henry Ford, Charles Lindbergh, and Henry Cabot Lodge. And guess what they called themselves? America First.”

At that time, the phrase was used by Lindbergh and others in conjunction with their support for Nazi Germany, but the Trump team has maintained that its adoption of the phrase has nothing to do with that past connotation.

McCain criticized Trump’s position on trade, calling the United States’ withdrawal from the Trans-Pacific Partnership the worst decision the country has made in a very long time. He said it would allow China to take over trade in the Asia-Pacific.

“I never met an isolationist who didn’t say, ‘I’m for free trade but I’m for fair trade.’ Never,” McCain said, paraphrasing Trump’s own talking point.

He also said Trump should reach out more to Democrats, develop a security strategy for dealing with Russia and China, and “stop tweeting.”

McCain reiterated his call for a select committee to take over the investigation of Russian interference in the U.S. political system and allegations of collusion between Russia and the Trump campaign. McCain said that some ties between Russia and Trump associates are certain, but the importance of those ties and their effect on the campaign was still unknown.

“We need a select committee,” he said. “We need to get the brightest people either outside of the Congress or inside the Congress, put them together and give them the charter. Because right now, there’s great skepticism as to whether the Congress can conduct an investigation in a thorough and efficient fashion.”

The Wednesday news conference by House Intelligence Committee Chairman Devin Nunes (R-Calif.), in which he alluded to incidental collection of communications of Trump associates, added to McCain’s concerns about Congress’s ability to get the job done.

Overall, McCain’s session was a full-throated endorsement of active U.S. engagement abroad and an effort to reassure the assembled Europeans that the United States would not abandon its historical role as leader of the free world and guarantor of the liberal Western world order.

Embedded in that message was an acknowledgement that Trump’s foreign policy is still a work in progress and that there are no guarantees which way it will go.