Do midterms naturally favor Republicans or the party out of the presidency?

[pbrower2a]

(Color based upon the Party of the President)

2014 -- huge R gains against a President with middling approval
2010 -- huge R gains against a President with middling approval, changing the majority party
2006 -- huge D gains against a President rapidly becoming unpopular, changing the majority
2002 -- slight R gain in the wake of September 11
1998 -- slight D gains, but not enough to undo the R majority
1994 -- huge R gains against a President with middling approval, changing the majority party
1990 -- slight D gains strengthening the D majority
1986 -- slight D gains strengthening the D majority
1982 -- slight D gains strengthening the D majority
1978 -- slight R gains but not enough to change the D majority.

If there is any pattern, Americans seem to like split government.

[pbrower2a]

The Republicans have a clear advantage in dark money in the last two midterm elections. But events mean much.

I see Barack Obama and Ronald Reagan almost as mirror images of each other... but neither could stop erosion of Congressional support for them.

Dubya was already looking like a disaster in 2006.