Just stop voting for them. Simple as.

Except, they have the huge advantage of incumbency. And isn’t it better to have somebody on your side win, no matter how severely reduced their mental capacity, than to potentially hand the election to the other side by voting for some unknown upstart? Same logic as not voting for a third party candidate who actually represents your views, basically. Vote for the lesser evil that everybody is going to vote for, because the good/younger candidate won’t win because nobody will vote for them.