It doesn't always work that way.
Republicans have bashed their own too if they have been found to do things they should not have, where democrats usually come to the defense of their own when they do something they should not. The Gov. of Illinois is about the only exception I know of.
Republicans and democrats alike were openly disgusted in Larry Craig and Mark Foley but democrats never minded that Barney Frank ran a homosexual prostitution ring out of his apartment, and its just homophobic if I even bring it up they would tell me.
The difference is Larry Craig and Mark Foley are gone, kicked out by their own party... Barney Frank on the other hand is protected by his own party and they will attack you if you even mention his homosexual brothel.
I think what the thread starter meant was when are the democrats are going to be consistent. If you are going to bash someone for something then bash everyone for it, not just those in another party.
Well, Republicans do seem to be less forgiving of sexual misconduct, that is true. Partisan politics being that they are, though, the name of the game is usually to bash the other party while protecting one's own.
Going back to Lyndon Johnson, Democrats had no problem bashing a Democrat for having sent troops into an unnecessary war.
Jimmy Carter was roundly denounced by both parties when the economy went sour, with only a few die hards pointing out that the root of the economic woes was OPEC.
Democrats weren't happy with Clinton and the spectacle of him lying under oath to cover up a sexual tryst, even while saying that the affair was no big deal.
But, in general, it's Republicans who bash Democrats, and vice versa.