(CNN) As the Republican convention kicks off in Cleveland, the status of the race for the presidency continues to be advantage Hillary Clinton.

Little has changed in overall support for either candidate since the end of the primaries in mid-June, despite major moments in the campaign including Donald Trump's announcement of Indiana Gov. Mike Pence as his running mate, Clinton's endorsement by her main rival for the Democratic nomination, Vermont Sen. Bernie Sanders, and the announcement by the FBI that Clinton would not face charges for her use of a personal email server while secretary of state.

But one candidate has made gains since last month: Libertarian Gary Johnson. In a four-way matchup between Clinton, Trump, Johnson and Green Party candidate Jill Stein, Clinton carries 42%, Trump 37%, Johnson 13% and Stein 5%. That represents almost no change for either Clinton or Trump, but a 4-point bump for Johnson.

Typically, support for third party candidates fades as the major party tickets are set heading into their conventions. But Johnson's support outpaces that of a typical third party candidate and may prove to have more staying power.

One hint that it could fade: Support for both Johnson and Stein appears concentrated among those less enthusiastic about voting this year, suggesting their supporters may be less apt to turn out in the end. Nearly 4-in-10 voters who say they are "not at all enthusiastic" about voting this year say they back either Johnson or Stein, but among those who are extremely enthusiastic, that figure falls to just 6%.

And the growing support for third party candidates also seems centered among younger voters, which could prove harmful to Clinton's campaign. Among those voters under age 35, 46% back Clinton, 21% Trump, 20% Johnson and 10% Stein. Broad support among younger voters helped catapult Barack Obama to the presidency in 2008.

As Trump prepares to accept his party's nomination, the poll suggests he's increased his backing among Republicans. The share of GOP voters who say they'd prefer Trump as the nominee over someone else has increased from 51% in June to 56% now.

In a two-way matchup, Clinton tops Trump 49% to 42%.

Both Clinton and Trump have bumped up their support among those who did not back them through the nomination process. Among those who say they'd rather see Sanders become the Democratic nominee, 79% now back Clinton, up slightly from 74% in June, while 74% of those who want someone other than Trump to be the Republican nominee now back him, up from 67% in June. Though Johnson peels support away in both groups when the four-way matchup is asked.

Other recent polling, conducted before Sanders' endorsement of Clinton and after the announcement that she would not face charges for her use of private email, found a tightening race, with independents shifting away from Clinton. In this poll, independent voters were more apt to back her in the two-way matchup than they were last June, but in a four-way contest, her support among independents is steady.

Clinton's continued lead may be due to the advantages she holds over Trump in likability (43% of voters nationally have a favorable view of Clinton vs. 39% who view Trump positively), experience (64% say she has the right experience to be president, double the 32% who say so about Trump), and on a range of issues including foreign policy, health care, abortion and race relations.

But Trump remains more trusted on the two issues atop voters' priority lists: The economy and terrorism. He holds his widest edge over Clinton on handling ISIS, and also holds an edge on handling taxes. Voters are also more likely to see Trump as sincere in what he says (49% say so vs. 41% for Clinton).

And Clinton continues to face widespread questions about her honesty and trustworthiness, 65% say they don't see her as honest, up from 50% who said so as news about her private email server broke in March of 2015. And although more say they'd be proud to have her as president than say so about Trump, nearly 6-in-10 say they wouldn't be proud should Clinton win the presidency.

Trump's newly minted running mate, Pence, receives a tepid welcome to the race, 43% say he's an excellent or pretty good pick, below the majorities who said so in initial surveys following the announcement of Paul Ryan in 2012, Sarah Palin in 2008 or Dick Cheney in 2000.

Almost 8-in-10 say his selection won't make much difference in the way they vote in November, though those who say it does matter say Pence makes them more likely to back Trump than shy away from the presumptive GOP nominee.

Those numbers may shift, however, as a majority say they don't know enough about Pence to have an opinion on him when they're asked if they have a favorable or unfavorable impression. Still, 53% say they believe he is qualified to serve as president if necessary and 57% say the choice of Pence reflects favorably on Trump's ability to make important presidential decisions.

On the recent spat between Donald Trump and Supreme Court Justice Ruth Bader Ginsburg, those who have heard about the back and forth generally say both acted inappropriately. Just under half say Ginsburg was wrong to criticize Trump, while roughly the same share say it was inappropriate for Trump to call for her resignation in response.