The presence of third-party candidates in the 2016 presidential campaign chips away at Hillary Clinton’s support slightly more than Donald Trump’s, according to new analysis from the latest NBC News|SurveyMonkey Weekly Election Tracking Poll.

The results show that Clinton loses slightly more support nationally with the existence of third-party candidates. Libertarian Gary Johnson and Green Party candidate Jill Stein share about 15 percent of the vote nationally in a four-way race that includes Clinton and Trump. But when the third-party candidates' supporters must choose between only Clinton and Trump, they split for Clinton at slightly higher rates than the GOP nominee.

The question is whether those who say they will vote for a third-party candidate are really non-voters who are just expressing dissatisfaction with the major party choices. Past survey research has shown that explicitly naming third-party candidates on questionnaires considerably overstates their actual support on Election Day.

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The poll--which asks all respondents both a two-way presidential vote question and a four-way vote question that included Johnson and Stein -- reveals that, when forced to choose between just two candidates, Johnson’s supporters pick Clinton at a slightly higher rate than they do Trump (39 percent to 35 percent). Stein—who holds just 4 percent of the vote nationally—sees her supporters breaking for Clinton in a more significant manner—57 percent to 18 percent.

The poll was conducted online from September 5 through September 11.

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With extremely high unfavorable ratings (Clinton at 59 percent, Trump at 60 percent), the popularity of third-party candidates has been the topic of a lot of debate this election cycle. Johnson, who has enjoyed around 11 percent support in the past few weeks, claims is he the answer to voters’ dissatisfaction with both major party candidates. Stein—who has consistently held on to about 4 percent of the vote—has tried to woo over progressive Bernie Sanders supporters after his defeat in the Democratic primaries. The open question is how much support they will actually receive on Election Day.

While the data show that the third-party candidates are hurting Clinton more than Trump, we know very little about the supporters of Johnson and Stein mainly because most traditional polls do not have large enough samples sizes to analyze these groups. The large number of respondents in the NBC News|SurveyMonkey Weekly Tracking poll allows for a closer look at where Johnson and Stein seem to be making headway with voters; they may also show where Clinton and Trump have vulnerabilities with certain groups of voters.

Perhaps the most encouraging number for Johnson is that he is winning the pure Independent vote. Among Independent voters who do not lean toward either party, Johnson claims a sizable lead with 31 percent support. Equal shares break for Clinton (24 percent) and Trump (24 percent), and Stein pulls in 12 percent

Even among Independent voters, there still is a significant gender gap that favors Clinton.

While Independent voters who are men break for Johnson by 12 points over Trump—37 percent to 25 percent—Independent voters who are women favor Clinton by 3 points (27 percent) over Trump (24 percent), and Johnson (24 percent).

Among voters overall, Johnson scores the most support among young men under 50. Though male voters are a key group for Trump and Republicans traditionally, 19 percent of young male voters currently say they support Johnson. Clinton does far better with women voters of both age groups.

The bottom line is that the third-party candidates have the potential to play a key role in the 2016 presidential contest. The open question is whether these third-party supporters will turn into actual voters in November.

The NBC News|SurveyMonkey Weekly Election Tracking poll was conducted online September 5 through September 11, 2016 among a national sample of 16,220 adults who say they are registered to vote. Respondents for this non-probability survey were selected from the nearly three million people who take surveys on the SurveyMonkey platform each day. Results have an error estimate of plus or minus 1.1 percentage points. For full results and methodology, click here.