Apparently you don't realize that although he was an adulterer, like Clinton and Kennedy, he was also a pretty good governor and had a pretty good record while in office.
He did not commit a crime, like Clinton and Kennedy did. Nobody died or was disbarred because of his actions.
We're not electing saints, nor are we beatifying or deifying politicians. Personally, the majority of Republicans preferred that he didn't run again, but we don't live there and have no say in what SC voters do.
But he didn't have his lover on staff, like Democrat NJ Governor McGreevey did.
His mistriss wasn't an executive with a bank his committee oversaw, like Barney Frank's male lover was.
Now, you might also find that many conservatives would have preferred that Vitter had resigned or not run again, and the same with Larry Craig, but, ultimately, they cannot be forced to resign, nor can their constituents be forced to not vote for them.
But what we don't do, which liberals do, is excuse their any and every action, no matter how egregious.