Once you prove you can get elected, you develop a level of inertia that keeps getting you elected.
Well, I think the key factor that determines who gets elected and who gets to stay in office in the U.S. is money and pandering to the oligarchs, who have been ruling this country for a long time now.
The whole “democracy” thing is little more than a show, if you ask me.
There are plenty of reasons for this mess: starting with the Constitution itself, through the absurd Electoral College and two-party system and the corrupt Supreme Court, all the way to unlimited campaign donations and the fact that there is no free press.