U.S. Senator John McCain McCain | Win McNamee/Getty John McCain to Donald Trump: ‘Stop tweeting’

Senator John McCain, chair of the United States Senate Armed Service Committee, has three pieces of advice for President Donald Trump.

Chief among them is “Stop tweeting.”

Also making the cut are “Reach across the aisle” in the style of Ronald Reagan, and “Listen to these very bright and intelligent people on his national security team.”

The advice was delivered in a discussion on “American Power” at the Brussels Forum, a high-level foreign policy and security conference.

McCain delivered the advice here in Brussels rather than the Oval Office because, he admitted, he’s never met with the President.

That’s despite a congressional military oversight role and his position as a former Republican presidential candidate.

Instead, McCain achieves his influence through the side door: “I speak almost daily to (Defense Secretary) Mattis and (National Security Adviser) McMaster,” he said.

McCain said he worried about the role of Russia in the 2016 American elections.

“I don’t think they succeeded” he said, “but the fact that they tried” can be “a death blow to democracy because it’s based on free and fair elections.”

McCain quotes Chairman Mao: "It's always darkest before it goes totally black." #BrusselsForum — Josh Rogin (@joshrogin) March 24, 2017

McCain added that while Russia may not be directly influencing the Trump administration, “the question is who does the president listen to when he tweets at 6am in the morning?”

He also said it was “disgraceful” that the United States does “almost nothing” as President Putin menaces Georgia, and that Brexit would be viewed in history books as a mistake.

Sen John McCain to UK 'people will look back on Brexit as a mistake' #BrusselsForum #brexit — Nik Gowing (@NikGowing) March 24, 2017

Embracing the need for changes at NATO, McCain told the audience there’s a need for a “new NATO” to address “new challenges.” That includes Montenegro becoming the alliance’s next member in McCain’s view.

NATO reform is different from marginalising the alliance, the Senator said.

In speaking about the citizens of NATO allies who died on the battlefield in recent years, he added: “I’m not sure how you put a price tag on that but it’s quite a contribution if you ask their mothers.”