While a challenger's presidential campaign can quickly adjust and adapt to shifting seas like a speedboat, an incumbent's campaign behaves more like a battleship, maneuvering slowly and making very large waves.
If there were contested general elections in every political race, there would be no talk of mandatory term limits because the voters would have a greater ability to vote out of office those who did not deserve to be there.
We change now for change's sake, hoping that somehow it is not insanity for us to repeat ourselves but that one of these new leaders will provide anything besides rhetoric and/or going through the motions.
While many things are working against Democratic incumbents this year, the public's tendency to be risk averse may make the difference in allowing some incumbents to win campaigns that they might otherwise have lost.
Only 8% of Americans want their representative in Congress re-elected. Normally, you need a boat load of cash to run against a member of Congress. Right now, all you might need is to just not be an incumbent.