For the first time in a while, not one but two third-party candidates are getting traction in the U.S. presidential race. Libertarian Party candidate Gary Johnson is polling from 7 to 12 points in general election polls, and Green Party candidate Jill Stein from 2 to 5 points — that’s at least one-tenth of the voters between them, and as much as one-sixth.

Although minor candidates tend to see their support shrink as the election nears, in a tight race each could take enough votes from one of the major candidates to give the election to the other.

The RealClearPolitics average gives Clinton a 2 point edge over Trump, with Johnson taking 9 points and Stein 3. If the election were held today, and Johnson’s voters went to Trump while Stein’s went to Clinton, Trump would win 49.9 to 44.8. But there are a lot of ifs.

What’s Happened Before?

In 1948, a divided Democratic party chose the unpopular Harry S. Truman, who had become president when Franklin Roosevelt died 82 days into his fourth term. One faction, upset with Truman’s support for civil rights, formed the States Rights Democratic party (the “Dixiecrats”) and nominated South Carolina senator Strom Thurmond. The other faction, upset with his Cold War policies, shifted to the recently formed Progressive party and its candidate, former vice president Henry Wallace.

Democrats worried that the two together would take enough votes from Truman to shift the electoral college to give Republican Thomas Dewey the presidency. They wouldn’t need to get many votes to tip some states to Dewey.

Thurmond drew only a little over one million votes (Truman got over 24 million and Dewey almost 22 million) and carried only four southern states and 39 electoral votes. Wallace got almost the same number of votes, but his support was spread across the country and he carried no state. Truman won with just under 50 percent of the vote and 303 electoral votes. Neither third-party candidate mattered at the end.

Most minor candidates have rarely cracked one percent of the vote, but at least a couple have tipped elections before. In 1968,the former governor of Alabama, George Wallace, who had been a lifelong Democrat, ran as the American Independent Party candidate and received 13.53 percent of the vote. It is believed he took enough votes away from Democratic candidate Hubert Humphrey to allow Republican presidential candidate Richard Nixon to win — by about 1 point.

In 1984, independent John Anderson took 6.6 percent and Libertarian Ed Clark 1.06 percent of the vote, not enough to stop Republican Ronald Reagan from winning the presidency.

Reform Party candidate Ross Perot fared the best of minor candidates in recent years, achieving 18.9 percent of the vote in 1992. He was widely perceived as having taken enough votes away from George H.W. Bush to tip the election to Bill Clinton. Perot ran again in 1996, but only received only 8.4 percent of the vote, not thought to have had an effect on the outcome.

What Will Happen This Year?

The question this year is whether come election day enough voters will be so turned off by Clinton and Trump that they’ll vote for a third-party candidate in high enough numbers to turn the election. The two major candidates have record high combined negatives.

Johnson is a somewhat conservative Libertarian, so if he were not in the race, it is possible most of his votes would go to Trump. However, he’s socially liberal on some issues, so Johnson voters are far from the GOP’s for the taking if Johnson’s support tanks in the runup to election day. Stein is a progressive, so if she were not in the race, most of her votes would probably go to Clinton. It’s also possible that if Johnson and Stein were out of the picture, many of their voters would either vote for another minor candidate or not vote at all.

The polls give different answers — and the answers are confusing. A recent Quinnipiac poll of voters in the battleground state of Florida found that including Johnson and Stein in the list of candidates did not affect the results. Without them, each of the two leading candidates got 47 percent of the vote, with only 2 percent saying they’d vote for someone else. With the two third-party candidates included in the poll, Trump and Hillary each got 43 percent.

But here’s part of what’s confusing: While only 2 percent had said they’d vote for someone else when only Trump and Clinton were included, 10% said they’d vote for someone other than Trump or Hillary when Johnson (8 percent) and Stein (2 percent) were included in the poll question. They’ll both be on the Florida ballot, but will voters consider them or focus on the two major candidates?

The same is true in two other battleground states, North Carolina and Ohio, according to the same poll. In both states Clinton wins by 4 points whether or not the other two candidates are included. In Ohio, however, the inclusion of Johnson and Stein increases Trump’s lead from one point to four — even though Johnson takes 14 percent of the vote and Stein six.

In at least one state, the two candidates may tip the balance, according to the latest polls. In normally Republican-voting Arizona, a Washington Post-SurveyMonkey poll found that Clinton edges out Trump by 46 percent to 45 percent in a two-way race. But with Johnson and Stein in the race, Trump takes the lead by two points, while Johnson comes in at 13 percent and Stein at four percent.

But The Electoral College

But the most important reality, as Cliston Brown notes in The Observer, a New York City weekly published by Trump’s nephew, is that Johnson and Stein probably won’t affect the electoral college numbers, and those are the numbers that elect presidents. Speaking of the fourteen states thought to be in play, the candidate who leads in the head-to-head vote is also leading when the two third-party candidates are included. Brown estimates that “On average, across the 14 competitive states, the third-party effect is benefitting Trump by about 0.25 percent.”

Yet that could change. A significant stumble by either major candidate could send some of their supporters to Johnson or Stein, enough to shift the vote in one of the close battleground states. Their presence allows disaffected Clinton or Trump supporters to participate in the election while feeling they’re voting on their principles, rather than just voting for the major candidate because they have to.

The third-party candidates could affect the race in another way: by changing the debate and forcing the major candidates to deal with their issues. If either minor candidate can reach 15 percent support in polling, he or she will be eligible to participate in the presidential debates. If Johnson is invited to the debates, he could become as significant a third-party candidate as Ross Perot was in 1992, due to the heightened publicity.

Coming soon: Rachel Alexander’s profiles of minor presidential candidates Gary Johnson and Jill Stein.