George Washington thought he was and should be replaceable.
What are you going to do if Louis walks in front of a bus tomorrow?
With term limits you try to create a system that imperfect people can not crash. You have new ideas being floated rather then stagnation.
Without term limits you have things like "Ted Kennedy's seat" and Robert Byrd being wheeled out on a gurney to "vote".
The Senate and House were not meant to be life long jobs.
I realize all that. But the answer is not MORE LAWS.
To hell with more laws. We have too many already.