Hillary Clinton’s laugh is so often transparently forced and insincere that it is a staple of Kate McKinnon’s impression of her on “Saturday Night Live.”

At the Democratic debate in Las Vegas, though, the former secretary of state let loose a long peal of amused delight and relief that had about it a strong hint of genuineness. Vermont Sen. Bernie Sanders had just said we had heard enough about her “damn e-mails.”

The crowd erupted in a standing ovation. Sanders had the signature line of the night, and it was in the cause of buttressing his opponent. He had put away the e-mail issue for the debate, perhaps for the duration of the primary campaign.

If Joe Biden was sitting at home plotting his electability case against Clinton based on her ethics, the episode had to give him pause. Democrats evidently have about as much interest in delving into Hillary’s e-mail and related controversies as they do in re-litigating Bill Clinton’s impeachment.

Las Vegas was a reminder that it is awfully hard to lose a nomination if no one truly plausible, let alone formidable, is running against you. The structure of the Democratic race from the beginning has been about propping up Hillary Clinton, and it still is. The party is putting on a master class in how to nominate someone under FBI investigation, and is in willful denial about her vulnerabilities.

Yes, Hillary had a good night. She was polished, knowledgeable, shrewd and hard-hitting — clearly, not someone to be trifled with. But the debate was a false indicator of her strength.

First, consider her competition (so far). Three former officeholders with nothing better to do, and one current officeholder who was crazy enough to launch a no-hope bid that has caught fire in the precincts of progressive America, but who isn’t taken seriously as a general-election candidate, and probably never will be.

The CNN debate was like Jeb Bush swooping in and dominating a debate against Jim Gilmore, George Pataki and Lindsey Graham, and everyone concluding he’s a marvelous performer.

On top of their plausibility or lack thereof, Hillary’s opponents have an instinct for the capillary, not the jugular. Sanders wants to argue that she isn’t socialist enough. Lincoln Chafee wants to go after her hammer and tongs on an Iraq War vote from more than a decade ago. Martin O’Malley wants to make the case against her on something or other. And Jim Webb wants to prove her unsuitability for the Democratic Party circa 1948. If she can’t handle these challenges, she is truly in a meltdown.

Second, Las Vegas wasn’t much of a road test of the issues bedeviling her candidacy, especially the e-mail scandal.

Outside of the friendly confines of the Democratic debate hall, it will continue to be pursued by the media, the GOP and, most importantly, the FBI.

Clinton remains a hostage to fortune in what the Feds conclude about the lawfulness of her private server and e-mail arrangement, and what is yet to be found on her e-mails.

Finally, Hillary Clinton’s problem is not Democrats. She has lost some altitude with them, and Sanders is a real threat in the early states. But it’s with the rest of the voters that she’s been tanking.

There is a drastic split between how her party and the rest of the country considers her. Sixty-eight percent of Democrats say she is honest and trustworthy in the latest CBS poll; 61 percent of all voters say she is not. She has a 69 percent-19 percent favorable/unfavorable rating among Democrats; among the general public, she is badly upside down, with a 33 percent-53 percent favorable/unfavorable rating.

In the latest Fox poll, she loses nationally to Donald Trump, Bush, Carly Fiorina and Ben Carson. Yet Democrats consider her the most electable of their candidates. It’s not a great tribute to Hillary Clinton that they are right.

Rich Lowry is the editor of the National Review magazine of conservative commentary.