2 year Presidential Terms

[LabourJersey]

Given midterm elections, I think this would be very chaotic and the incumbentt would tend to get swept out all the time unless we just won a world war or landed on the moon or something similarly unifying. 

I think the opposite actually. There would be no midterms, and thus no midterm dynamic. Every election is a general election.

Plus as I understand it in states with 2 year gubernatorial terms it's not particularly common for incumbents to lose their first re-election?