David Goldman / AP

HEMPSTEAD, N.Y.—Donald Trump faced one overriding test in Monday night’s long-awaited debate with Hillary Clinton.

And by all indications he flunked it—emphatically.

Heading into the debate, leading strategists in both parties had identified the same priority for Trump: reducing the historically unprecedented number of voters who say he is not qualified to be president. But Trump’s frequently rambling, disjointed, and vague answers, and his impatient and sometimes brusque demeanor, likely did more to reinforce those perceptions—especially when contrasted against a performance from Hillary Clinton that was fluid and competent, if not particularly inspiring.

In a country so deeply polarized, there’s no guarantee Trump’s unsteady performance will produce big changes in polls now showing a close race nationally with Clinton, or that any immediate changes would endure through Election Day. But by solidifying doubts about his temperament and competence, the debate likely will heighten the hurdles Trump faces in extending his support beyond his beachhead at, or just above, 40 percent in most surveys.

In a campaign that has often seemed to pivot on which candidate’s weaknesses are in the spotlight, Monday’s debate kept the doubts about Trump’s preparation, discipline, and fitness far more in the foreground than the parallel concerns about Clinton’s honesty and sincerity.

“Instead of clearing them, Trump tripped over his own hurdles,” said one frustrated Republican strategist after the debate. “He got tired of acting presidential and he showed little command of issues, outside of trade. To be fair to Trump, Clinton did not have to answer any hard questions about her own record, so you have to figure in the next debate the moderator will try to even the scales.”

Many Trump supporters view his lack of conventional political credentials, and his unpredictable nature, as an asset: proof that he’s an agent of change who will disrupt a political system they view as ineffective and tilted against them. But beyond his base, doubts about Trump’s ability to handle the presidency—particularly the responsibilities of commander in chief—have been a persistent headwind for him.

Across multiple surveys before the debate, roughly 60 percent of Americans said they did not consider Trump qualified to be president. An instant post-debate poll conducted by CNN/ORC showed that Trump failed to make any meaningful progress in reducing that number. In the survey, just 43 percent of those polled said that, based on Trump’s performance in the debate, he could “handle the job of president if he is elected.” A solid majority of 55 percent said he could not. By contrast, 67 percent of those surveyed said Clinton could handle the job, while just 32 percent said she could not. By 68 percent to 27 percent, those surveyed also said Clinton had demonstrated a better command of issues. Although CNN acknowledged its sample leaned excessively toward Democrats—which may itself reflect a statement about which side felt good enough about the debate to respond to polls about it—those remained decisive advantages.

Doubts about Trump’s qualifications loom as a particular obstacle for him with college-educated white voters. The principal reason Trump has struggled to grow his support much beyond 40 percent is that he is facing unprecedented resistance with those white-collar whites: The national surveys released over the past week by NBC/Wall Street Journal, ABC/The Washington Post, Bloomberg Politics, and Marist/McClatchy all showed Clinton leading Trump among college-educated whites. No Republican nominee in the history of polling dating back to 1952 has lost those well-educated whites.

Few goals rank higher for Democrats than preventing Trump from recovering with those voters; just before the debate, longtime Democratic strategist Joe Trippi, the campaign manager for Howard Dean in 2004, said, “Isn’t that the whole thing for tonight? If you can preserve that [as Clinton], you win. Or if you can make that happen [as Trump], you win.”

The full answer to the debate’s impact won’t be apparent until more detailed surveys weigh in. But the instant CNN poll—and the reaction from strategists on both sides watching the candidates’ performances—suggested the encounter mostly reinforced the white-collar doubts about Trump. While 68 percent of college whites in the post-debate CNN survey said Clinton was qualified to be president, 57 percent said Trump was not. Two-thirds of them picked Clinton when asked which candidate had shown the greatest mastery of the issues.

“Right from the start, he seemed grossly unprepared for a serious discussion,” Joel Benenson, Clinton’s chief strategist, maintained after the debate. “I think he became unraveled during it. … I think on the temperamental side he reinforced the sense that this guy just doesn't have the temperament to be president, and on the substantive side I think he came completely unprepared for what is the biggest job in the world.”

Given the underlying divisions in the electorate, Benenson said, it was unclear whether the debate would increase the share of voters who view Trump as unqualified. “But,” he added, “I think it certainly reinforced any images for people who held that [view] on the way in."

Through the campaign so far, each campaign has largely sublimated policy critiques to sustained efforts to brand the other as unfit for the presidency. In its opening moments, the debate seemed like it might break that pattern. Trump spoke directly to his blue-collar base with a slashing attack on trade deals and pledges to punish American companies that move jobs overseas; those proved his most forceful moments of the evening, even if they likely induced heartburn for many congressional Republicans and their allies in business institutions like the U.S. Chamber of Commerce.

Clinton, unsteady in her response on trade, pivoted to firmer ground by making a familiar Democratic argument against Republicans that has been surprisingly muted in her campaign to date: the charge that Trump’s economic plan represented a version of trickle-down economics that would mostly benefit rich people like himself.

But before long, the debate shifted back to the terrain on which both sides have seemed most comfortable: challenging the other’s qualifications, ethics, and temperament. And on that front, Clinton dominated the discussion, especially as the debate proceeded and Trump seemed to palpably lose steam (notwithstanding his attacks on Clinton’s “stamina”). “I thought he passed the test well in the first half,” said John Brabender, the chief strategist for Rick Santorum during the 2012 and 2016 presidential primaries. “In the second half, he spent too much time explaining and answering the question asked rather than delivering his message and transitioning the discussion to where he needed it to go.”

After his August stumbles, Trump has battled back to narrow the race, largely through his dominant performance among working-class white voters. And while even those voters said in the CNN poll that Clinton had displayed more mastery of the issues, a solid 57 percent majority said Trump had shown he could do the job as president. That was one of several indications in the poll that Trump’s turbulent night was unlikely to significantly erode the support he has attracted so far.

But history suggests the share of voters now saying they will support Gary Johnson or Jill Stein will decline as the election nears. That means the ultimate winner will likely need to attract a larger share of the vote than Trump today is drawing in almost any survey, and Clinton is failing to reach in most. And it is on that front the debate may vex Trump most.

Monday night offered the two candidates the largest audience they have addressed so far, and possibly the largest audience they will reach at any point before Election Day. Trump’s inability to make more progress against the lingering doubts about his experience and temperament represented a huge opportunity cost. The big question now is whether he has now cemented that predominantly negative impression—or can reverse those doubts in the two remaining debates.

Reporter Leah Askarinam contributed to this story.

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