If character is indeed destiny, Mr. Weiner’s fate was sealed long ago. His narcissism was profound and undisguised. His tantrums on the floor of the House could be epic. His serial use of social media to engage in sexual byplay with women — apparently without actually having sex with them — turned him into a national joke. So did his chosen nom de porn: Carlos Danger. His family name became a weapon New York tabloids used mercilessly, if predictably, to make him the butt of one salacious pun after another.

To put it bluntly, Anthony Weiner — smart, often witty, politically deft, at one time plausibly a strong candidate for New York mayor — proved to be a pathetic jerk. But few jerks do as much damage as he did in his recklessness. He may even be responsible for Donald Trump being president.

Days before the Nov. 7 voting, the F.B.I. director, James Comey, announced he was reopening his investigation into Hillary Clinton’s use of a private server for her emails as secretary of state. Mr. Weiner was the reason. During their investigation of his sexting, federal investigators had found a trove of emails on his home computer that was also used by his wife, Huma Abedin, one of the Democratic presidential nominee’s closest aides.

In the end, the Feds found nothing. But damage had been done. Mrs. Clinton has said the Comey announcement, coming so late in the campaign, was a big reason she lost the election. That is debatable, but the polling analyst Nate Silver, for one, has said she is probably right.

Regardless, the extent of the fallout from Mr. Weiner’s character flaws is stunning.

In the courtroom where Mr. Weiner was sentenced sat his parents and his brother. His wife was not there. She filed for divorce in May — more wreckage from his behavior. In her book “What Happened,” Mrs. Clinton described how “Huma looked stricken” on learning that Mr. Comey’s new focus on those emails was a byproduct of the federal investigation into Mr. Weiner’s texting habits. Mrs. Clinton wrote that Ms. Abedin burst into tears and said, “This man is going to be the death of me.”