Americans love third-party candidates...until election day

Given that Donald Trump and Hillary Clinton are the least popular presidential candidates in modern history, you might think there’d be an opening for a third-party candidate, someone promising to transcend partisanship and find new solutions to America’s enduring problems.

The lead contender is probably Libertarian Gary Johnson, a widely respected former Republican who served two terms as governor of New Mexico and who’s within striking distance of the 15 percent polling numbers he needs to join the official presidential debates.

But if history is any guide, Johnson is unlikely to gain support over the coming months. No third-party contender in the modern era has ever improved on his or her summertime polling numbers, going all the way back to Strom Thurmond’s Dixiecrat run in 1948.

In June 1968, the leading third-party threat came from George Wallace, a law-and-order, anti-civil rights presidential candidate running on the American Independent Party ticket. But his 17 percent polling numbers shrank below 14 percent by November. Twelve years later, when the consummate centrist John Anderson made a run as an independent, he posted early poll numbers around 24 percent before ending up a distant third to Republican Ronald Reagan and Democrat Jimmy Carter. Even independent business mogul Ross Perot — generally considered the most successful third-party candidate in recent history — lost nearly half his support between June and November 1992.

There’s a good reason third-party candidates tend to fade with the fall leaves: The real cost of a third-party vote gets clearer as the election nears. In June, it’s easy to pledge support for a third-party candidate — particularly for voters who feel fatigued after the bruising primaries and are eager to express dissatisfaction with their major-party choices.

But an actual vote is different, especially when the election looks close and the third-party candidate is poised to play the spoiler. Say you really do want to see Johnson in the White House, but you feel just as strongly about preventing a Clinton victory. Unless you think Johnson has a legitimate chance, you might well abandon him at the last minute and pull instead for the candidate with the best shot at toppling her, namely Trump.

To really build support, in other words, Johnson has to seem not just appealing but also viable. And that’s difficult. It would require a fairly dramatic political realignment. Say if Trump’s penchant for controversy takes a turn for the even-worse, turning lukewarm Republican support into outright defiance. Or, from the other side, what if one-time supporters of Bernie Sanders refuse to line up behind Clinton — despite Sanders’ endorsement?

Johnson does have some natural advantages. Unlike Perot or Ralph Nader, he has extensive governing experience, further bolstered by the his running mate, two-term Massachusetts governor Bill Weld. And his libertarian platform includes a rare mix of policy preferences, including more welcoming immigration policies, far lower tax rates, protection of abortion rights, and a laissez-faire approach to global warming — all part of a more consistent “get the government out of the way” approach to economic and social issues.

One early test will be Johnson’s ability to crack the 15 percent polling barrier and join the official debates. That big stage might be his best chance to introduce American voters to his distinctive blend of policy preferences, or his penchant for mixing left-leaning ideas (like marijuana legalization) with right-leaning ones (like school choice), while sprinkling in some government reforms (like term limits).

Absent that, Johnson may be end up as the latest in a line of third-party spoilers, with no hope of capturing his own electoral votes but a good chance of getting in other candidates’ way. And since he’s a former GOP governor, that probably means siphoning off support from Trump. If he captures enough disgruntled Republicans in southwestern states like New Mexico or Utah — near his home turf — that could boost Clinton’s electoral tally, possible giving her the crucial edge or turning a victory into a landslide.

Then again, there is a countervailing force. On the left, Green Party candidate Jill Stein is mounting her own third-party effort. And her votes are likely to come at Clinton’s expense.

This is the real impact of third-party candidates in American politics. They don’t win elections, or even come close. But they do sometimes decide the outcome, with huge consequences for the course of American history. Need an example? Just ask Al Gore.