Anthony Weiner announced his resignation from the House only a day ago, but already, a backlash is building among Democrats who wonder why their party moved so forcefully to shove aside one of its own.

True, Mr. Weiner’s offense was tawdry. Tweeting pictures of your own person to young women is highly questionable behavior for a married politician. There’s no question Weiner did it, because of ample electronic evidence. And he publicly lied about his actions for days.

But didn’t another Democratic politician do much the same thing a few years ago? Yet the party closed ranks around Bill Clinton.

Weiner, they pitched under the bus. Democrats from Barack Obama on down said the New York lawmaker should seek other employment.

That’s the theory, anyway.

“A politician may resign out of embarrassment, as Representative Anthony Weiner did, but that doesn’t justify other politicians from his own party, including the president himself, calling for his resignation,” writes John B. Judis, a senior editor at The New Republic.

Well, that’s one point of view. But we can think of some reasons that Democrats turned on Weiner, and not on a certain philandering president.

Mr. Clinton was powerful. Weiner wasn’t. Is this too obvious? Clinton held a post that used to be called leader of the free world. Weiner was 1/435th of the House. It would have been a huge deal for the Democratic Party to push out a president, especially one as politically adroit as Clinton. It’s much easier to turn on an embarrassing Democrat who is one vote among many.

Politics is brutal. If the above section sounds a little, well, chilly, then perhaps you have not noticed that politics is a profession for the thick-skinned. Professional loyalty goes only so far, and the direction it usually goes is up. There is little tolerance in Washington for misbehavior in the lower ranks. Everyone who has worked in official D.C. for any length of time knows stories about staffers whose jobs vaporized overnight due to some real or imagined indiscretion. Worker bees are expected to conduct themselves in a manner that’s best for the hive. Perhaps Weiner’s fate should be seen in that context.

Clinton had more friends. Through decades in public life, Clinton had acquired a huge network of personal friends and people who owed him favors. An appearance at a fundraiser here, a note to a financial supporter’s mom there, and suddenly you’ve got a support system that partisan institutions don’t provide. Clinton was great at this. By all accounts, Weiner was not as good. That his colleagues said little positive about him in the days following the incident is telling.

Still, some on the left side of the political spectrum are saying that Weiner resigned too quickly. Josh Marshall at Talking Points Memo is one. He argues that the drumbeat of calls for Weiner’s resignation was unprecedented and that Weiner’s offense was silly compared with the thievery and so forth in which the political system abounds.

“[T]hat disconnect – the most insistent and open demands for resignation ever compared to one of the silliest scandals ever – just doesn’t sit right with me,” writes Mr. Marshall in a TPM blog.