Sen. John McCain (R-Ariz.) listens to testimony during a Senate Armed Services Committee hearing on March 14, 2017. (Tasos Katopodis/AFP/Getty Images)

Sen. John McCain has not met Donald Trump in years, McCain said Friday, a measure of the degree to which the president has frozen out his most biting Republican critics.

McCain (R-Ariz.), who has sharply attacked Trump’s message on a host of international issues, most notably his approach to Russia, is a former GOP standard-bearer who remains chairman of the Senate Armed Services Committee. His exclusion from the Oval Office may suggest that Trump is focusing on wooing allies already sympathetic to him while spurning dissenters, even if they could potentially provide political cover and support.

“I have not talked to the president,” McCain said at the Brussels Forum, a conference organized by the German Marshall Fund of the United States. “I met him some years ago. I have not met him since.”

McCain said he speaks almost daily to Trump’s national security team, including Defense Secretary Jim Mattis and national security adviser H.R. McMaster. But the Republican senator added that he was “not positive who the president listens to,” and he expressed worry that Stephen K. Bannon, Trump’s chief political strategist, was more influential than the president’s more conventional foreign policy hands.

McCain’s comments come at a delicate political moment for the president. Trump has struggled — and, so far, failed — to assemble a workable Republican coalition to pass an overhaul of the Affordable Care Act. Though McCain’s criticisms focused more on international affairs than domestic policy, the splits over health care have made clear that Trump still needs to woo all sides of his fractious party if he is to enact his ambitious political agenda.

McCain, asked what advice he had for Trump, told him to “stop tweeting” and to reach across the aisle.

In trying to explain many Republicans’ avoidance of world affairs, he cited prominent Americans known for isolationist views in the 1930s. McCain pointed to Henry Ford and Charles Lindbergh as examples of a persistent strain of isolationism in U.S. politics.

McCain repeated a call for a “select committee” to investigate alleged ties between the Trump campaign and the Kremlin. “Right now there is great skepticism, actually, as to whether Congress can conduct an investigation in a thorough and efficient fashion,” he said.

“This is a most serious issue,” McCain said. “The question is how significant were those ties.”

His call for an independent investigation came after Rep. Devin Nunes (R-Calif.), chairman of the House Intelligence Committee, said he had briefed Trump on the committee’s probe, prompting critics to charge he was acting more like an advocate for the president than an independent investigator.

“It’s bizarre,” McCain said.