Yes, he lied. But the situation is not the same as Weiner's.
Somebody dug up dirt on him from years' earlier. Weiner was caught "live"; as was Chris Lee.
Chris Lee resigned within four hours. Weiner went on Liar's Tour of the Major Media.
Vitter is old news at this point - and what he did was less egregious than Clinton's Lewinsky Affair, which the Dems defended as being Private Business. There's no evidence that Vitter received blow jobs from a prostitute in his Congressional office while talking on the phone handling government business.
But Vitter is useful in the 'who's is blackest' game, the "he started it" game, the "he did it too" game and "you can't accuse anybody of anything if you've ever done it yourself" game. Since none are without sin and all have fallen short, it is a very useful tactic for lowering the bar until you don't require any form of veracity, character, or virtue from those elected to high office.
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