Reporting from Washington  —  As the first debate of the presidential campaign approaches, voters are in an increasingly frustrated and unhappy mood, driven to their choices more often by dislike of the opposing candidate than admiration for their own, new polling data find.

Nearly 6 in 10 voters described themselves as frustrated by this year’s campaign, according to newly released data from the nonpartisan Pew Research Center. That’s up from just under half earlier in the summer. More than half called themselves disgusted.

Only about 1 in 4 voters reported positive feelings about the election, saying they were optimistic (15%) or excited (10%), a share that was heavily outweighed by those who are flat-out scared (43%).

Separately, a new analysis of tens of thousands of voter interviews by SurveyMonkey underscores how much unfavorable impressions of one candidate or the other are driving voters’ choices.

About 38% of American voters like Clinton and have an unfavorable view of Trump, the analysis found. On the flip side, 34% like Trump and dislike Clinton.

The slight difference in the size of those two groups accounts for Clinton’s small, but persistent, lead in most polls.

Caught in the middle are roughly 1 in 4 voters who view both candidates unfavorably. About 7% of voters dislike both, but dislike Trump more; an equal number dislike Clinton more; and about 10% dislike both with equal fervor, SurveyMonkey found.

Voters on both sides increasingly see a Trump win as a possibility — and that may get more people to vote »

Those who like one candidate and not the other are firm in their vote choice and say they are very likely to vote, the analysis found.

Those who dislike both candidates are much less certain of their vote choice — or even whether they will vote at all. They tend to be younger and are more likely to call themselves independents. And they account for a lot of the ups and downs in polls that have been seen in the last few weeks.

The negative feelings many voters have about the candidates came through in how they described their presidential choices, Pew found.

Asked to state in their own words why they supported their candidate, voters often focused on the faults of the other side.

“I don’t like him — he seems arrogant and egotistical,” wrote one 44-year-old woman who said she nevertheless planned to vote for Trump. “He’s the lesser of the evils I’m seeing for this year’s election. But not by much.”

“I am opposed to Hillary Clinton. I believe she is corrupt and a liar,” wrote a 67-year-old man explaining why he backed Trump.

A 35-year-old woman on the other side wrote: “I don’t fully support Hillary Clinton for president, but she does have the experience, and really there is no other option. The concept of Trump as POTUS is terrifying.”

A 61-year-old man cited “her diplomatic experience and my intense opposition to Donald Trump.”

Overall, about a third of both Trump and Clinton supporters said the main reason they supported their chosen candidate was that he or she wasn’t the other one, Pew found.

For Trump supporters, “he is not Clinton” was the most-cited reason, followed closely by Trump’s outsider status and his own positions on issues. For Clinton supporters, “she is not Trump” was tied with her experience in government as the most mentioned reason to vote for her.

Detailed results from the USC Dornsife/L.A. Times daily tracking poll »

Asked separately to say which of a list of possibilities was a major reason, a minor reason or not a reason to vote for their candidate, roughly two-thirds on each side cited dislike of the other candidate as a major reason.

Among Trump supporters, the only two items more often cited than dislike of Clinton as a major reason to vote for him were his views on terrorism and the economy.

Among Clinton supporters, her experience in government and her leadership ability, along with a dislike of Trump, were the top items cited as major reasons to back her.

Although Republican elected officials who are equivocal about Trump often describe their vote as a choice to “support the party’s nominee,” relatively few Trump voters picked that as a major reason for their vote — only 28%.

By contrast, 48% of Clinton’s voters cited her status as the party’s choice as a major reason to back her. The gap between the two parties on that question reflects the greater unity within Democratic ranks in this election.

The two groups of voters also show very different priorities on issues. While Trump’s voters listed his position on terrorism as one of their top reasons for backing him, Clinton’s voters pointed to her position on race relations, a subject cited as a major reason by only about 1 in 4 Trump supporters.

The Pew analysis was based on 4,538 American adults, including 3,941 registered voters, surveyed from Aug. 16 to Sept. 12. It has a margin of error of 2.6 percentage points in either direction for the registered voter sample. The SurveyMonkey analysis was based on 14,373 American adults polled by the firm Sept. 12-16.

David.Lauter@latimes.com

For more on Politics and Policy, follow me @DavidLauter

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