A Republican member of Congress says he's going to vote for Libertarian nominee Gary Johnson — not Republican nominee Donald Trump — in this fall's presidential election. Retiring Rep. Scott Rigell (R-VA) told the New York Times on Friday that he was unable to support either Trump or Democratic nominee Hillary Clinton. He predicted that Trump will suffer more Republican defections before the November election.

In any other election year, this would be a shocking development. Party loyalty is a powerful force in American politics, and the Libertarian party has never been taken seriously in mainstream politics.

But Donald Trump's inflammatory comments and erratic behavior have tested the partisan loyalty of Republicans across the country. At the same time, most Republicans also can't stand the Democratic nominee, Hillary Clinton. Which makes Johnson — a former Republican governor who agrees with Republicans on a broad range of economic issues — a natural alternative for those who are disgusted by Trump's behavior.

Donald Trump has put Republican leaders in an awkward position

Ordinarily, Republicans are expected to offer unconditional support to other Republican candidates. The problem is that Trump is no ordinary candidate. His campaign has been a steady stream of provocative statements about women, Muslims, Mexicans, and other groups.

At this point, many Republicans have nonetheless held their noses and endorsed him anyway. The conventional wisdom has held that they don’t have much choice. Trump’s leading rival, Hillary Clinton, is unacceptable to most Republicans. And while there was some discussion among conservatives about organizing a third-party bid for the presidency, it’s now too late for that. Key filing deadlines have passed in a number of states, including states like Texas and Florida that would be crucial to any conservative candidacy.

Yet it’s worth noting that there is another option here. There’s already a former Republican officeholder who will be on the ballot in most and possibly all 50 states: former New Mexico Gov. Gary Johnson.

Johnson isn’t a perfect candidate from a conservative perspective. Most notably, he favors abortion rights. But he’s a lot more conservative than Hillary Clinton, and he would likely prove a more reliable conservative in the White House than Donald Trump.

Many Republicans endorsed Trump earlier this year on the assumption that he would start acting more like a conventional politician once he had the Republican nomination in hand. But his weeklong feud with the parents of fallen American soldier Humayun Khan removed any remaining doubt that Trump is going to clean up his act.

So Republicans like Rigell are starting to take a second look at Johnson, the one presidential candidate who has actually governed as a Republican.

Johnson is the most orthodox conservative in the race

It’s easy to find issues on which Johnson is out of step with most other Republicans. He’s pro-choice, favors LGBTQ rights, and wants to liberalize drug laws (He's a former marijuana user himself). He’s also considerably less hawkish than other Republican officeholders. Johnson doesn’t share the stridently anti-immigrant policies of many current Republicans (although he would have been right at home with the more immigrant-friendly GOP of the George W. Bush years).

Still, Johnson and mainstream conservatives are on the same page on a lot of other issues. Johnson is an orthodox fiscal conservative. He favors tax and spending cuts. He's a defender of gun rights.

In New Mexico, he proposed expanding educational choice with school vouchers. He favors abolishing the Department of Education. He's a critic of Obamacare and George W. Bush’s expansion of Medicare to cover prescription drugs.

On many of these issues, Johnson’s conservative record is longer and more consistent than Trump’s. In 1999, Trump said he was "very liberal when it comes to health care," favoring "universal health care." He once supported an assault weapons ban and a longer waiting period to purchase firearms. He has also generally shown little interest in cutting government spending.

More importantly, there’s every reason to believe that Johnson actually believes in the largely conservative agenda he’s running on. Trump, in contrast, doesn’t seem to believe in much of anything beyond his own self-interest and hostility toward foreigners. While Trump has made a lot of promises to conservatives, there’s simply not much reason to think he would actually deliver on those promises once he reached the White House.

Johnson has a better shot than most third-party candidates

Ordinarily, third-party candidates have a slim chance of getting elected, and 2016 is no exception. But the unusual characteristics of this race mean that Johnson is less of a long shot than the typical third-party candidate.

Third-party candidates face a chicken-and-egg problem: Everyone assumes they can’t win, so political and media elites ignore them, reinforcing the perception that they can’t win. The last third-party candidate to break out of this vicious cycle was Ross Perot, who wound up with 19 percent of the vote in 1992.

Johnson is currently polling at about 7 percent, one of the best showings for a third party since Perot’s 1992 run. And his major party opponents are wildly unpopular. Hillary Clinton is viewed unfavorably by a whopping 54 percent of voters. Trump is disliked by an even more remarkable 58 percent of voters. Those numbers are far worse than previous major party candidates.

So there are a lot of voters who would be open to voting for a third candidate if they thought he had a good shot at getting elected. And Johnson — unusually for a Libertarian candidate — has taken few positions that would turn off mainstream voters.

So if Johnson does start to move up in the polls — and especially if he clears the 15 percent threshold for inclusion in the presidential debates — he could appeal to a fairly broad swath of voters: orthodox conservatives who are dissatisfied with Trump’s policy views, centrists who appreciate Johnson’s combination of social liberalism and fiscal conservatism, and voters who are equally disgusted by Trump’s outrageous statements and Clinton’s cozy relationship with special interest groups.

Indeed, if Trump continues to make self-destructive comments and Republicans respond by endorsing Johnson, Johnson could wind up as the de facto Republican standard-bearer.

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