In presidential campaigns, third-party candidates lose — badly and often.

"There are two generalizations we can make: Third party candidates usually don’t do very well, and the other thing is that their support tends to fade as the campaign goes along at the end," says Jonathan Ladd, a Georgetown University political science professor.

But Donald Trump and Hillary Clinton are such uniquely unpopular candidates that maybe this year is the year of the third-party candidate. Maybe now is the time for Libertarian Party candidate Gary Johnson to sweep in and have a real impact.

And maybe headlines that hype them are onto something — after all, neither Clinton nor Trump is as close to 50 percent of the electorate as he or she might like. Johnson’s numbers do look high — and stable — for a minor-party nominee at this point in the campaign.

But there is a lot of history working against Johnson. Measured against the benchmarks of previous third-party candidates, and what political science says about Johnson’s chances in the race, this year might very well turn out to be just like years past. Ultimately, however, votes for Johnson serve more as a referendum on how polarized the two major parties have become — or how strong the dream of third-partyism is to voters.

This year is different. Or is it?

With two extraordinarily unfavorable major party candidates in Trump and Clinton, minor party candidates have been getting a lot attention. We’ve seen the stories.

There is some truth to the idea. Green Party candidate Jill Stein’s numbers are negligible, but Johnson is polling higher than most minor party candidates do at this point in the general election — at 8.5 percent of the vote.

While most minor party candidates fade throughout an election season, Johnson has seen an increase since his June poll numbers — which hovered around 4 or 5 percent of the vote — and now remains consistently around 8 percent. Historically, this late in the game, most minor party candidates don’t drop too much more in the polls, according to FiveThirtyEight’s polling model. It’s possibly Johnson can carry his support until Election Day, Harry Enten writes:

Most third-party candidates didn’t lose that much support between late summer and Election Day … The average drop-off is about 2 percentage points … Johnson was projected to finish with 6.5 percent of the vote in mid-July when he was polling slightly higher than he is today. Now, the model is projecting that Johnson will win 7.1 percent of the national vote on Election Day.

But there is a hard truth with minor party candidates. As Ladd suggested, minor party candidates don’t usually do as well as the polls may suggest. And sure, while Johnson is doing better than recent third-party runs, that success is relative. It’s unlikely he will meet the 15 percent threshold to even appear in the general election debates starting September 26 — let alone surpass Ross Perot and actually win a state.

Ballot access doesn’t seem to be a barrier for him. Johnson is currently on the ballot in 46 states and the District of Columbia. And according to the Libertarian Party’s website, he is in the process of getting on the ballot in the remaining states. Stein is only on the ballot in 38 states and DC.

Even so, most people voting for third-party candidates know it isn’t a winning vote. There is no pre-prescribed condition for third party success, plainly because in modern politics third parties haven’t won presidential elections. And relative success is so rare, each candidate has an individual story. Johnson’s lead is instead representative of the unprecedentedly large ideological gaps between the two major party candidates.

Clinton and Trump are extremely polarizing candidates. Voters are sharply ideologically divided on policy issues, Center for Politics’ Alan Abramowitz found. Political animosity is at a high; 55 percent of Democrats are "afraid" of the Republican Party; and 49 percent of Republicans are afraid of the Democratic Party, according to a Pew poll. In that environment, a third-party candidate could be a welcome choice.

Support for third-party candidates historically tends to fade by Election Day

Consider two presidential election polls. The first includes both major political parties and minor party candidates: Clinton, Trump, Stein, and Johnson. The second poll excludes Stein and Johnson, only listing major party candidates.

The first more closely resembles the Election Day ballot in November. The second will more accurately gauge Election Day results, according to Ladd.

Currently, general election polls without Stein and Johnson put Clinton 5 points above Trump, with 46 percent of the vote on average. When pollsters include Johnson and Stein, Clinton has roughly 42 percent of the vote, leading Trump by around 4 points.

There is a notable — now tired trope — from the late American political historian Richard Hofstadter on third-party candidates: "Third parties are like bees. Once they have stung, they die," Hofstadter wrote in 1955.

Historically, minor party candidates sting early in the race, and, to stretch Hofstadter’s metaphor, they die slowly until Election Day. "Third parties tend to lose, their poll numbers tend to decrease over time, and they perform worse on Election Day," John Sides, a political scientist with George Washington University, tells me.

Take Perot in 1992: the most successful modern-day minor-party candidate to date. Perot, a wealthy Texan businessman who ran as an independent with a plan to eliminate the deficit, led both Bill Clinton and incumbent former President George H.W. Bush in the polls for three months leading up to the conventions.

Then Perot began to fade. "The conventions remind regular voters why they are Democrats or Republicans," Ladd said of Perot’s decline in support.

Perot temporarily suspended his campaign in July of 1992, and restarted it again in October. On Election Day, Perot won 19 percent of the vote — one point less than polling projections — behind Clinton and Bush. He didn’t win a single state. As president, Clinton eventually took on eliminating the deficit, absorbing the policy idea that made Perot so popular.

Overall, Perot’s trajectory is consistent with other minor-party campaigns (The New York Times has a good visualization of this.) In 1968, third-party candidate George Wallace, who ran on a segregationist platform, won 14 percent of the vote on Election Day, despite polling around 17 percent a few months prior. It’s a "pattern of third-party support fading as people face the prospect of a wasted vote," Dartmouth College political scientist Brendan Nyhan tells me.

In other words, as Election Day nears, the reality of a presidential vote dawns on American voters who had once expressed support for third-party candidates. They tend to cast their ballot strategically, voting for the lesser of two evils.

Johnson seems to be bucking off the fade

Despite this trend, Sides is a little more "bullish" on third parties with Johnson this year than in most election years, he tells me.

The conventional wisdom — as outlined by several political scientists and by Enten’s FiveThirtyEight piece — attributes Johnson’s relative success to Clinton and Trump’s unprecedentedly high unfavorablity ratings. In other words, voters hate the leaders of the major parties so much that the idea of casting a ballot for the lesser-of-two-evils candidate is too much an ask.

Andrew Gelman, a statistician and political science professor at Columbia University, has another theory:

"Perot in 1992 received 19 percent of the vote but won zero states. That election was not close, which perhaps made people feel more free to vote for a third party. I'd guess that the opportunity for third-party success in 2016 is again if the election does not seem like it will be close," Gelman tells me. As general election polls stand now, Clinton has a comfortable lead over Trump.

Either way, third-party candidates do best when they stand out from the pack, when they have a "persona that neither party can quite emulate quickly," Sides said. Potentially, Johnson has room for growth if he puts together a more prolific fundraising operation. Johnson seemed to be picking up his fundraising operation in August, raising more than $2 million in the first two weeks — more than any other Libertarian presidential candidate has raised in one month. But to really make a dent, he might need to do much better than that.

"Perot, he bought 30 minutes of air waves with his pie charts or whatever, to talk about the budget," Sides said, recalling Perot’s political infomercials. Perot paid for screen time to explain his economic ideas. "You need a message to stand out as a party and the resources to get out the message," Sides added. So far, Johnson hasn’t done much of that.

Johnson won’t win the presidency, but that’s not the point

But, even with all this hype over Johnson, it’s important to keep things in perspective. It’s highly unlikely that Johnson will be able to break the threshold to appear in the televised presidential debates — let alone win a state during the general election.

"Trump is obviously quite different than anything we’ve seen before, [but] we should be cautious about throwing past data out the window," Nyhan said. "Many aspects of this election will still look a lot like previous ones."

Even if Johnson does better than other third-party candidates in recent years, the impact on major party candidates remains minimal. Robert Erikson, a political scientist and general election polling expert, explained it to me this way:

In the current comparisons of the responses to the two versions [of polls, one including minor-party candidates, and the other excluding them], Clinton's lead seems to shrink about a point on average. This would be normal if third-candidate defection rates from the two major candidates are the same. For instance, suppose Clinton leads Trump 50-40. With [Johnson] added, [there’s a] 10 percent defect. Clinton goes to 45, Trump to 36. A 1-point gap becomes nine. But nothing much really changes.

Hype around Johnson raises another point: Election year after election year, we find ourselves reconsidering the third-party question. There is always anger toward the two parties, and in this election, Trump presents yet another complication for voters that traditionally vote Republican.

As my colleague Timothy Lee explained, if Johnson finds a national platform, he would appeal to a wide range of people: "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," Lee writes.

Overwhelmingly, people who vote for the third party tend to do it for ideological reasons — because they are interested in the third party as an idea. They know their candidate will lose, but they simply cannot cast a ballot for the major party nominees. To vote for a third party on Election Day therefore becomes a referendum on polarization among major party candidates — a measure of just how ideologically off-base Republicans and Democrats have to get for a minor party candidate to break through.