Here are key moments from the third and final presidential debate between Democrat Hillary Clinton and Republican Donald Trump, Oct. 19, in Las Vegas. (Sarah Parnass/The Washington Post)

Here are key moments from the third and final presidential debate between Democrat Hillary Clinton and Republican Donald Trump, Oct. 19, in Las Vegas. (Sarah Parnass/The Washington Post)

When the final presidential debate between Hillary Clinton and Donald Trump started, it seemed as if it might be the best of the three and certainly Trump’s best. By the end, it was the story of Trump in Campaign 2016 in microcosm, a series of angry exchanges, interruptions, insults that served to undercut the good he might have accomplished earlier.

In the opening minutes on Wednesday night, Trump seemed a different candidate from the Trump of the first two debates and the unshackled Trump on the campaign trail. He was more subdued, more focused on policy and substance, effective in making the case for himself and against his opponent. He appeared to have disciplined his worst instincts.

But that was only for a time. Then he became the campaign trail Trump, irritable when criticized, unwilling to accept the assessment of the intelligence community about Russian interference in the election, denying the accusations of nine women who said he had groped or kissed them against their will, and repeatedly lashing out at his rival.

Finally, it was the Trump who in the past few days has railed against a rigged election system. Asked directly by moderator Chris Wallace of Fox News whether, if he lost, he would accept the outcome of the election as legitimate, he hedged. He would decide at the time, he would “keep you in suspense.” It was, as Wallace suggested, an unprecedented departure in the history of the country. It was also a major mistake. Yet Trump seemed not to care at all.

[Trump won’t commit to accepting election results if he loses. Clinton says thats ‘horrifying.’]

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In that sense, this final debate was what everyone expected, a repetition of what has come before. The likelihood is that it will do little to alter the trajectory of the campaign and that leaves Trump in a perilous position.

Clinton came to the last debate leading in the polls and looking to expand the electoral map. Yet the 90-minute forum was no cakewalk for her. She not only took fire from Trump, she took tough questions from Wallace on issues that had been treated lightly in the first two debates.

In some ways, when the focus was on the issues, whether abortion or immigration or taxes and spending, the debate might have been judged as the most even of the three. Certainly partisans on each side no doubt saw a decisive performance by their candidate.

It was remarkable how the two could carry on serious debate about some issues — what to do in the Middle East, the state of the Affordable Care Act — and then be so personal in their attacks almost with the next breath, as when Trump, near the end, uttered “such a nasty woman” as Clinton was talking about Obamacare.

Clinton could afford to play mostly to her constituency, given the state of the race. Trump needed to do more than make those in his coalition who most dislike Clinton cheer his attacks. But as he has repeatedly in the campaign, Trump managed to undermine his best moments with his worst, likely leaving him short of his goal — if it was his goal — to bring new voters to his side.

[Clinton, Trump made 24 notable claims at last night’s debate, and we fact-checked them]

Through the course of the debates, Clinton has expanded her lead over Trump. Her margin in national polls has increased from about three points just before the first debate to an average of about seven points at the time the candidates took the stage Wednesday night on the campus of the University of Nevada at Las Vegas. The same has happened to her advantage in the electoral college, to the point that Trump has no easy or obvious path to the 270 votes needed to win the election, short of a dramatic turnaround.

The Fix’s Aaron Blake breaks down the key moments of the third presidential debate on Oct. 19 between Hillary Clinton and Donald Trump. (Bastien Inzaurralde/The Washington Post)

Polls and projections on the eve of Wednesday’s debate consistently estimated Clinton with enough states in her column to put her well over 270. Equally concerning for Trump is the fact that the remaining competitive states, in addition to predictable swing states that have consistently been battlegrounds in recent elections, include a handful of traditional Republican strongholds.

Arizona appears the most attractive target for Clinton among those red states. The Clinton campaign will send first lady Michelle Obama to Arizona on Thursday in an effort to take that state away from Trump. Georgia also appears competitive, though perhaps harder than Arizona for the Democrats.

Then there are Texas and Utah. Texas will be exceedingly difficult for Clinton to win, but three recent polls surprisingly put Trump’s margin in low single digits there. And then there is Utah, where Trump’s bombast has turned off voters and independent Evan McMullin’s candidacy scrambles the state of play.

Jim Messina, Obama’s 2012 campaign manager, made a telling observation during a panel discussion here on Tuesday night, pointing out the degree to which this campaign threatens to shatter the GOP’s southern block of states and create an almost solid blue line up and down the East Coast.

Messina noted that almost the entire Eastern Seaboard, from Maine to Florida, could end up in her column on Nov. 8, particularly if Clinton were able to widen her current lead. South Carolina is the one exception, still presumably for Trump. Other Southern coastal states — Virginia, North Carolina, Georgia and Florida — are either in play or already tilting strongly toward the former secretary of state.

That’s not to say all this will come to pass, only that at this point that Trump has managed to squander — through self-inflicted wounds — whatever assets he seemed to have before his latest descent began. He has run an undisciplined campaign, replete with wild charges, the promotion of conspiracy theories and fights with members of his own party. He did so again Wednesday night.

His travel schedule suggests either that there is no electoral map strategy inside his campaign or that Trump has overridden the advice of his advisers. He was in Colorado on Tuesday, rather than Arizona. He was recently in Wisconsin, which looks out of reach at this point. He will be in Ohio and Florida and North Carolina over the next few days, but also plans a stop in Virginia, despite no objective evidence that he has much chance there.

The debates have brought to a close an important chapter in the campaign. Trump and Clinton will continue to take aim at one another on the campaign trail, but the window for persuading voters is closing quickly. With voting now underway in a series of states and with more states to begin soon, the focus will increasingly shift to the more granular competition of turning out every vote.

Here too, Trump’s campaign is at a huge disadvantage, dependent either on the candidate’s ability to rouse organically a silent army of voters who have stayed on the sidelines in recent elections and will materialize at the polls this year or, more realistically, on relying on efforts by the Republican National Committee to function as his get-out-the-vote operation.

All of that may be immaterial to Trump. He will chart whatever course he chooses during the final 19 days, as he has done since he first announced his candidacy, as he did again in the final debate. But this election remains Clinton’s to lose and Trump hasn’t found a way to change that equation.