Ex-McCain aide: Trump has 'unstable personality'
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A former top aide to Sen. John McCainJohn Sidney McCain10 factors making Russia election interference the most enduring scandal of the Obama era Earth Day founder's daughter: Most Republican leaders believe in climate change in private Trump gives nod to vulnerable GOP Sen. McSally with bill signing MORE (R-Ariz.) said that presumptive GOP presidential nominee Donald TrumpDonald John TrumpTrump calls Sri Lankan prime minister following church bombings Ex-Trump lawyer: Mueller knew Trump had to call investigation a 'witch hunt' for 'political reasons' The biggest challenge from the Mueller Report depends on the vigilance of everyone MORE has an "unstable personality."

“He’s going to lose, and I think he’s got kind of an unstable personality to begin with,” Mark Salter said during Politico's "Off Message" podcast this week.

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Salter, a speechwriter for McCain's 2008 presidential campaign, last week tweeted he would back Democratic front-runner Hillary ClintonHillary Diane Rodham ClintonIt is wrong to say 'no collusion' 10 factors making Russia election interference the most enduring scandal of the Obama era And the winner of the Robert Mueller Sweepstakes is — Vladimir Putin MORE over Trump. His comments came after Trump cited a National Enquirer story that claimed Sen. Ted CruzRafael (Ted) Edward CruzTrump removes sanctions waivers on countries buying oil from Iran The Hill's Morning Report - Is impeachment back on the table? Buttigieg steals Beto's thunder MORE's (R-Texas) father was linked to Lee Harvey Oswald before the assassination of President John F. Kennedy.

"The GOP is going to nominate for President a guy who reads the National Enquirer and thinks it's on the level. I'm with her," he tweeted last week.

During Politico's podcast, Salter predicted Trump would "come apart ... in some kind of visible way.

“I think that's quite possible. ... I'm not a psychiatrist, but there is something wrong with [the] guy,” he said.

Even though Salter said he plans to support Clinton over Trump, he said he likely would be "disappointed" — but he emphasized that her presidency would still be an improvement. 

“I’m sure 10 minutes into Hillary Clinton’s inaugural address I’ll sort of be disappointed,” he said.

“[But] her foreign policy would probably be a modest to maybe substantial improvement over the incumbent. ... I’ve never voted for a Democrat for president in my life. But she is the more conservative choice and the least reckless one. She won’t — or at least she hasn’t said that she would — take the U.S. out of NATO. She hasn’t encouraged other nations to get their own nuclear weapons. She hasn’t threatened to slap a 45 percent tariff on imported goods.”

Salter said there's essentially nothing the presumptive GOP nominee can do to change his mind.

"He'd have to have a brain transplant," he said, when asked.