Surprising lack of one-term Presidents?

[Reaganfan]

With the back and forth divisions of politics in America the last 10-12 years, you would expect that our presidencies would be back and forth as well. After all, Congress has gone from GOP to Democrats to GOP in just four years, but we continue to have Presidents re-elected at an amazing rate. By all indications, George W. Bush should have lost re-election, then John Kerry would have had Katrina and the economic downturn, leading to the election of a Republican, then that President would have just lost re-election to a Democrat. Maybe something like this:::

Bill Clinton (1993-2001)
George Bush (2001-2005)
John Kerry (2005-2009)
McCain/Allen/Romney (2009-2013)
Obama/Hillary/Whoever (2013-)

My question is, why is it easier to sweep an entire congress out twice within four years, but nearly impossible to beat a President once in four years?

One thing of note...if only men voted...the results of the last 30 years of Presidential elections wouldn't be too different, except Bill Clinton and Barack Obama would have lost re-election. Is it possible that women voters and certain voting blocs make it next to impossible?