The longer they stay in Washington, the more leftist they become.
It is a disease and none are immune.
The longer they are there, the more their world becomes Washington and their ‘good friends from across the aisle’ than their constituents. From what I have read, Lugar hasn’t even have a residence in Indiana for decades. So, who was he actually ‘representing’?
Incumbency becomes like a bad fungal infestion. They get comfortable and fester.
The longer they are there, the more skeletons they accumulate that they don't want exposed.
Cute lobbyists, opportunities to trade on insider knowledge -- the skeletons don't get exposed as long as they do not piss off the Dems. It's just easier to play ball.