Most attention in the U.S. presidential race is going to Republican Donald Trump and Democrat Hillary Clinton. But two other candidates – Libertarian Gary Johnson and Jill Stein of the Green Party – are starting to get more attention. They are also rising in popularity in public opinion studies.

Both Johnson and Stein ran for president for their parties in the last election in 2012. Back then, public opinion studies showed Johnson had the support of four percent of voters. Stein got two percent.

Recent poll results show both candidates getting nearly two times that level of support in this election.

High voter unhappiness

Opinion surveys also show that more than half of Americans have negative views about Trump and Clinton. Political experts say this high level of dissatisfaction is getting more people interested in the Libertarian and Green Party candidates.

Robert J. Guttman is the director of the Center for Politics and Foreign Relations at George Mason University's Schar School of Policy and Government.

"Hillary Clinton having an untrustworthy factor of about 66 percent, Trump being even higher than that. We have two candidates out of 330 million Americans that are the most disliked I've seen in the 40 years I've covered politics."

It would be highly unusual for a candidate who is not Republican or Democrat to be elected president of the United States.

The last time this happened was in 1850, when Millard Fillmore became president as a member of the Whig party. Fillmore was serving as vice president under President Zachary Taylor and became president when Taylor died.

It is difficult for third-party candidates to compete with Republican and Democratic nominees. They do not receive the same organizational and financial support. The U.S. Electoral College voting system also favors major-party candidates.

But Johnson says he believes he has a chance of winning because of the "extraordinary" things that have happened in this year's campaign season.

But Johnson says he believes he has a chance of winning because of the "extraordinary" things that have happened in this year's campaign season.

The Libertarian candidate appeared this week in his second town hall broadcast on the television channel CNN. He appeared with his vice presidential running mate, Bill Weld.

"So really our strategy is to win this thing outright, and some extraordinary things have to happen," Johnson said. "But has there ever been a more extraordinary political year in our lives?"

Johnson is a businessman and former two-term Republican governor of the U.S. state of New Mexico. Weld served two terms as Republican governor of Massachusetts.

Libertarians agree with Democrats on some issues and with Republicans on other issues. The party's name comes from the word "liberty," which means the state of people living free in society.

The Libertarian Party is more liberal than the Republican Party on social issues like abortion and same-sex marriage. But the party has conservative views, too. It supports lower taxes, smaller government and less military involvement abroad.

"We want the government out of your pocketbook and out of your bedroom. And I will tell you the polling shows a majority of Americans think that," Weld said during the town hall event.

The Green Party is expected to officially nominate Jill Stein and her vice presidential running mate Ajamu Baraka in the coming days.

Stein is a Harvard-educated doctor and an advocate for environmental and health issues. Baraka is a longtime human rights activist.

Also running for the Green Party nomination is William Kreml, a professor of politics at the University of South Carolina.

CNN will hold a town hall broadcast on August 17 for the Green Party.

The Green Party platform calls for government action to protect the environment from global warming and for developing renewable energy sources. It also supports full access to abortion for all women, opposes the death penalty and calls for an end to corporate campaign donations.

One sure way to get noticed by millions of Americans is for Johnson and Stein to appear on the debate stage with Trump and Clinton. But debate rules require them to first get at least 15 percent support in multiple public opinion studies.

Johnson himself said "There's no chance of winning without being in the presidential debates."

Guttman said it is even possible that Trump might not participate in the debates. The Republican nominee has accused the Clinton campaign and the Democratic Party of trying to "rig" – or unfairly control – the debates.

"I think it's 50/50 if Trump will even show up. And if Gary Johnson – the Libertarian candidate who's on the ballot - gets I think it's 15 percent, so we could have Hillary Clinton debating Gary Johnson."

Along with trying to qualify for the debates, candidates Johnson and Stein are also trying to get on the voting ballot in all 50 states and the District of Columbia for the November election. Johnson is currently on the ballot in 36 states, according to the Libertarian Party's website.

Stein is currently on the ballot in 24 states and the District of Columbia, according to the Green Party's latest online map.

Even if Johnson and Stein do get on the all the ballots before the November election, they will face difficulties in getting votes.

In the 2012 election, Democrat Barack Obama received 66 million votes. He beat Republican Mitt Romney, who received 61 million. Johnson received just 1.2 million votes and Stein about 500,000.

But Guttman said 2016 is a very different political year. He expects both Johnson and Stein to do much better with voters.

"Republicans are turned off by Trump. Hillary has a high negative factor, and (Clinton Vice President candidate) Senator (Tim) Kaine from Virginia seems like the most grown-up person in the race. But most people don't vote for vice president. So yeah, this is a great year for a third-party candidate..."

He added that many voters are now "looking for alternatives like crazy." He said that means both Johnson and Stein could get more votes in this year's election than any other third-party candidates in U.S. history.

Some consider a vote for a third-party candidate a "wasted" vote, because the candidate has a low chance of winning. That could stop some voters from supporting Johnson or Stein. But, Guttman says, this is not a "normal year."

"In a normal year I would agree with that. But this is so far out of a normal year that I don't think people are going to think they are throwing their vote away."

I'm Bryan Lynn.

Chris Hannas reported this story for VOANews. Bryan Lynn adapted his story and did additional reporting for Learning English. Ashley Thompson was the editor.