There are term limits.
They are called elections.
Are you in favor of passing laws to protect the voters from having to exercise their duty to throw out the bad guys?
If term limits are a good idea for Presidents, they are also a good idea for Senators and Congressmen.
Saying that the longevity of lousy politicians is solely the fault of the voters overlooks the power of incumbency and of party political machines to rig elections in favor of the incumbent. If the party establishment wants to deny slush funds to someone challenging the incumbent, they can and will do so. They can also use their media connections to make sure that the incumbent gets all of the coverage while the challenger gets marginalized.