Presidents on a Roll?

It's hard to make generalizations about presidential administrations because there are relatively few cases in any given era, but they are on the verge of doing something that hasn't been done since the Monroe administration, and it has left me wondering what it might mean (if anything).

If the economy continues to turn around--which it is beginning to show signs of doing--and if presumptive Republican nominee Mitt Romney continues to offer a solid but uninspiring challenge to President Obama, it's likely that the president will be re-elected. 

And if that happens, it will be the first time since Jefferson-Madison-Monroe that three presidents in a row have sought and been re-elected to a second term.  The trio of Roosevelt-Truman-Eisenhower is the closest second, with FDR himself being re-elected three times and Truman serving most of Roosevelt's fourth term before being elected in his own right, but he did not stand for re-election in 1952, and probably would not have survived a challenge from IKE. 

It's even more interesting to note that Jefferson-Madison-Monroe were all in the same "Democratic-Republican" Party, while our recent three are far more diverse.  Clinton and Obama can each stake a claim to be centrists or moderates in their party--especially Clinton--but they are clearly cut from a different cloth than Bush. 

What does this mean?  Is it just coincidence?  Is it now harder somehow to beat an incumbent president?  Bush certainly seemed beatable in 2003, but in the end he was tough to dislodge.  Does it reflect something about our polarized politics?  Hypotheses welcome.