Even before Donald Trump found himself on defense for disparaging Sen. John McCain's military service, Sal Russo wasn't too impressed with the real estate mogul's presidential prospects.

Russo knows a thing or two about populist uprisings and anti-establishment candidates. The former Reaganite spent eight weeks advising billionaire Ross Perot's third party campaign in 1992. In 2002, he consulted for a conservative challenger to moderate Los Angeles Mayor Richard Riordan in California's Republican gubernatorial primary (his candidate won the nomination). A few years later, Russo founded Tea Party Express, a group he still runs.

On Saturday, Trump came under fire for questioning whether McCain's time as prisoner of war during the Vietnam War, during which he was severely tortured, qualifies the Arizona Republican as a war hero. The day before, in a telephone interview with the Washington Examiner from his home in Sacramento, Calif., Russo discussed the billionaire businessman/reality television star's upstart bid for the GOP presidential nomination.

Russo's verdict: The frustration with Washington and the political establishment that Trump has tapped into with his unorthodox, blunt style is very real and shouldn't be dismissed. Trump has risen in part by taking a hard line on illegal immigration. But the New Yorker's comments have been interpreted by some as broadly anti-immigrant, and Russo said that Trump's message lacks the substantive seriousness and positive, uplifting vision required to turn anti-establishment agitators, like President Ronald Reagan, into winners at the ballot box.

The interview with Russo was edited for length and clarity.

Examiner: What do you make of Donald Trump?

Russo: Both Trump and Bernie Sanders are taking advantage of abject frustration with the established order — on the left and the right. People think the system doesn't work. The manifestations are, of course, candidates that speak very boldly but not necessarily in ways that make them universally popular. The problem with their electability is, protest candidates aren't usually successful. Those that are successful articulate a vision for the future.

Examiner: Has Trump caught fire with Tea Party voters?

Russo: I would say no to that. We continually poll our donors to see what they're thinking and he has not polled very well.

Examiner: In 1992, you spent about eight weeks in Dallas advising Perot, another billionaire businessman rabble-rouser. Any similarities?

Russo: I don't think the overlap is clear with Trump other than the frustration and [voters] liking the blunt, straight talk. And Perot was pretty folksy — he was far less provocative than Trump.

Examiner: You live in California and witnessed first hand the 2003 recall of Gov. Gray Davis, which featured another celebrity-turned-politician in Arnold Schwarzenegger. Any similarities between that race and what you're seeing with the Trump phenomenon?

Russo: Schwarzenegger has the celebrity that Trump has, [although] in the campaign Arnold never said anything too provocative. That's where Trump — a lot of things he says strains credibility. He hasn't laid out an agenda where people can relate to it. But when you look at Arnold saying, 'I'm going to blow up the boxes,' nobody was offended by that. It was, okay, he's going to go up there and clean up. It's an important pivot point, credible even if unspecified. If voters like you and trust you they'll impute to you what they think should be done. But you need to be likable.

Examiner: Is Trump hurting the Republican Party's brand and jeopardizing the eventual nominee's chances against Hillary Clinton?

Russo: I would generally say no to that. I don't think anything is damaging particularly. The nominee defines the party. When we have a nominee that person is going to define the party and what the alternatives are. I hear all that hand wringing; I think it's pretty silly. I don't think it's going to matter. If Trump's on the ticket, it matters.

Examiner: Can Trump win?

Russo: We have never in modern times elected a protest candidate as president. The candidate with the more forward looking agenda has tended to win all of the time. So the big question is, can Trump turn his protest movement into something more appealing to the general public? The personality candidates seem to often be the protest candidates, which means there is a limited shelf life. People want a vision.