Ron Paul, whose 1988 Libertarian presidential bid and two Republican bids made him the "liberty movement's" best-known figure, told MSNBC today that he couldn't support Gary Johnson for president and saw reasons to back the Green Party's Jill Stein.

"If you tend to lean toward progressivism, you can lean toward the Green Party," Paul said. "She's probably the best on foreign policy."

It wasn't the first time Paul had suggested a vote for Stein over Johnson, who is polling higher than any Libertarian nominee in the party's history. "If you can't stand any of them and you happen to be a dedicated progressive, you ought to make your vote count and vote for the Green Party, and if you happen to be a libertarian, vote for the Libertarian Party," Paul told CNN in March.

At that time, Johnson and Stein were the clear front-runners for their parties' nominations. But since the LP's Memorial Day weekend convention, Johnson has run as a cross-ideological candidate, attempting to build "a six-lane highway between the two parties." When asked about the details of the Libertarian Party platform, he has made clear that he does not stand by all of it.

Paul hinted at his problem with that in the MSNBC interview. "He doesn't come across with a crisp Libertarian message," said Paul of Johnson. "I'm voting for the nonaggression principle."

That was a reference to a concept in libertarian thinking, and Libertarian Party politics, in which any initiation of force — to use police power to enforce environmental regulation, for example — is immoral. Johnson rejected it, while more radical Libertarians said it was fundamental to what the party stood for.

Paul has expressed these gripes with the Libertarian Party before. In 2008, he shunned the party's nominee, former Republican congressman Bob Barr, and endorsed Chuck Baldwin, the candidate of the far-right Constitution Party. (Paul appeared on Montana's ballot as that party's nominee.)

On Monday, Paul defended Johnson from televised stumbles on the details of foreign policy. "It shouldn't be disqualifying," he said. "When that is done, I'd like to ask the questioner some snap questions. Who's the current president of Switzerland, you know?"

In a statement, Johnson spokesman Joe Hunter brushed off Paul's quasi-diss.

"Gov. Johnson has long respected Dr. Paul, and supported him in the past," said Hunter. "But when we have the Republicans and Democrats criticizing Gov. Johnson for being too libertarian, and Dr. Paul suggesting he isn't libertarian enough, that probably arrives at a balance a great many voters can identify with. As for his comments about Dr. Stein, I suspect the size and scope of the government she envisions would be rather breathtaking to Dr. Paul."

Recent U.S. politics has favored candidates from the Democrat and Republican parties, but here are seven examples of candidates who ran under a different mantle. (Sarah Parnass/The Washington Post)