Some facts:
1. Since 1990, the Republicans have achieved over 50% in the popular vote in the Senate only 3 times: 1994, 2002, and 2014.
2. Since 1990, the Democrats have achieved over 50% in the popular vote in the Senate 7 times: 1990, 1992, 1998, 2004, 2006, 2008, and 2012.
3. There seems to be a "before and after" mark around 2005, where the margin between the Democrats and Republicans becomes more pronounced, in both the Senate % and the popular vote. From 1990 to 2004, the % difference was never more than 6%. After 2006, the % difference was never less than 5%, and with the exception of 2010, it was never less than 7%.
4. Since 1990, the Democrats have won the popular vote in the House in only two midterms, 1990 and 2006.
5. Since 1992, the Republicans have won the popular vote in the House in only two Presidential years, 2000 and 2004.
6. In every Presidential year since 1992, the House popular vote and % have been won by the political party that also had its Presidential nominee win their respective election.
1992: Clinton wins, Democrats win House % and popular vote. (And the most seats)
1996: Clinton wins, Democrats win House % and popular vote. (But not the most seats)
2000: Bush wins, Republicans win House % and popular vote. (And the most seats)
2004: Bush wins, Republicans win House % and popular vote. (And the most seats)
2008: Obama wins, Democrats win House % and popular vote. (And the most seats)
2012: Obama wins, Democrats win House % and popular vote. (But not the most seats)
7. In 1996 and 2012, both years which saw a Democratic president re-elected, the Democrats won the % and popular vote of the House, but not the most seats.
8. From 1996 to 2000, in three consecutive elections (1996, 1998, 2000), the House % and popular vote were extremely close. The % differences were all under 1.1%, and the popular vote differences were all below 750,000 votes.
These stats seem to make the midterm vs. presidential year trends look even clearer.
