Take off your Democrat/Republican hats for a while. Let's look at this logically.

Regardless of any intent of the 'Founders' I find the concept of 'lifetime politician' to be morally reprehensible. Sorry, but being Senator should not be a career. This is how power accumulates in Washington, and why most of our legislators are millionaires.

I propose the following:

Representative - 6 terms, 12 years
Senator - 2 terms, 12 years
President - 1 term, 6 years (can run again, but not for consecutive terms)
Supreme Court - 1 term, 18 years (President nominates one every two years)

Extra benefits (besides just the limitation) - the President is never distracted by running for re-election, and Supreme Court appointee finagling and 'strategic retirements' would be eliminated.

Just so we're sure no particular ox is being gored, the regulations could take effect beginning with the next-entering elected group. So, any of the old 'dinosaurs' would be grandfathered, and the clock could start anew.

An excellent treatise on the Supreme Court aspects of this issue can be found at:
Virginia Law Review article

What do you think?