If Donald Trump were a more disciplined candidate, he’d have plenty of fresh material to use against Hillary Clinton in their last debate, which will take place tonight, in Las Vegas. PHOTOGRAPH BY MARY SCHWALM / AFP / GETTY

It’s fitting that this year’s third and final Presidential debate will be held in Las Vegas. For Donald Trump, who during the nineteen-eighties and nineties built a short-lived casino empire in Atlantic City, Vegas has long represented the big time that he couldn't quite crack. Although he currently co-owns a high-rise hotel on the northern end of the famous Strip, he has never had any gaming interests in Nevada. Now it looks like Trump's Presidential ambitions, or, at least, the most widely watched manifestation of them, will come to an end in Sin City.

Rather than preparing for Wednesday night’s debate, an activity that taxes his short attention span, Trump has been on the road for the past couple of days, continuing the scorched-earth campaign he set out on last week, ranting about a giant conspiracy involving the "global power structure," a nefarious media, and the Hillary Clinton campaign.

Speaking in Green Bay, Wisconsin, on Monday night, he repeated his new mantra that the election has already been rigged. "They even want to rig the election at the polling booths, and, believe me, there's a lot going on," he said. In Colorado Springs on Tuesday, he dismissed the latest polls, which are almost universally awful for him, saying he didn't believe them anymore. "Believe me, folks," he said. "We're doing great. If we keep our spirit and if we go out and win, this is another Brexit, believe me."

If that sounded like whistling in the wind, it almost certainly was. Since early last week, when he declared himself unshackled after Paul Ryan, the Republican House Speaker, told his colleagues he would no longer publicly support Trump, the G.O.P. nominee has been on a tear, and there's no reason to expect him to stop now. Rather than trying to act Presidential on Wednesday night and appeal to voters in the middle, he will almost certainly flail away, seeking to tear down Clinton and cast doubts on the fairness of the election.

Evidently, some Trump aides have bought into the cockamamie theory that if their candidate can tar Clinton enough to turn off voters in sufficient numbers, turnout on November 8th will be so low that he might just scrape home. But other Trump loyalists appear to have had just about enough. On Tuesday, New Jersey Governor Chris Christie, who has kept a low profile over the past week, publicly distanced himself from the latest iteration of Trump. Asked by Kelly O'Donnell, of NBC News, whether he was proud of Trump's campaign, Christie replied, “The person who needs most to be concerned about the kind of campaign they’re running is the candidate. Because it’s the candidate’s campaign. It’s not my campaign.” Christie added, “I’m proud of everything I’ve said, and that’s all I can control. The rest of it I can’t control.”

The irony is that if Trump were a more disciplined and well-schooled candidate, he'd have plenty of fresh material to work with going into this last debate. Over the past week or so, e-mails published by WikiLeaks have shown members of Clinton's campaign staff cozying up to big donors, talking favorably about accepting money from lobbyists who work for foreign interests, and coördinating with friendly super PACs in a way that, on the face of it, looks like it might be the sort of behavior that campaign-finance laws are supposed to prevent. The Clinton campaign has claimed that the Russian government obtained the e-mails by hacking the account of John Podesta, the Clinton campaign chairman, but it hasn't challenged the veracity of individual messages.

Also in the past few days, the F.B.I. has released notes from interviews that the bureau carried out during its investigation of Clinton's private e-mail server. In one document, an unnamed F.B.I. official referred to a possible "quid pro quo," in which another F.B.I. staffer would look into the possibility of changing the security classification of a Clinton e-mail in return for a senior State Department official, Patrick F. Kennedy, supporting an F.B.I. request for more of its agents to be allowed into Iraq. Both the F.B.I. and the State Department have said no such deal was made, and the classification of the e-mail wasn't altered. Nevertheless, the release brought the Clinton server back into the headlines.

Finally, a couple of days ago, James O'Keefe, a conservative activist and filmmaker, released an undercover video of a Democratic operative, Scott Foval, boasting about planting Democratic supporters at Trump rallies and inciting violence, a practice he called "bird-dogging." O'Keefe is a dirty trickster. In the past, he has been accused of doctoring his videos to further his political agenda, and in 2013 he pleaded guilty to breaking into the office of Mary Landrieu, the former Democratic senator from Louisiana. On this occasion, though, his video had an immediate impact. On Tuesday, CNN reported that Foval had been fired from the group he worked with, Americans United for Change, and that Robert Creamer, an official at the Democratic National Committee who was in contact with Foval, had stepped down.

In the heat of a debate, how effectively will Trump be able to marshal this sort of material, which demands a command of specifics? The moderator, Chris Wallace, of Fox News, is a tough interviewer, and he’s sure to confront Trump with the allegations of sexual assault that have emerged over the past week. Will Trump give a short answer and try to move the discussion on to other issues, or will he do what he has done repeatedly in recent days: attack the women who made the allegations and, in some instances, criticize their appearances? Clinton’s campaign is surely hoping he pursues the latter course.

Clinton, for her part, will likely attack Trump for his loathsome treatment of women, as she did so effectively in the first two debates. But since she now has a healthy lead in the polls, she may also spend more time trying to strike a positive note and laying out her extensive policy agenda. The format of the debate may lend itself to such a strategy. Running for ninety minutes, the back-and-forth, at least in theory, will be divided into six segments: debt and entitlements, immigration, the economy, the Supreme Court, foreign hot spots, and fitness to be President.

During the first two debates, particularly the second, which was a biff-bang-wallop affair, we didn't hear very much about the economy and other domestic issues. Tonight's event will give the candidates a third and final chance to articulate their overarching philosophies and explain their key proposals. In a campaign that has seldom failed to shock, that would be yet another surprise: a substantive and even-tempered discussion of important differences.

Don't hold your breath.