Silver takes a very early look at 2014 Senate races:
Keep in mind that in each of the last four cycles, one party (Democrats in 2006, 2008 and 2012; Republicans in 2010) won the vast majority of the competitive races. If Republicans swept all the “lean” and “tossup” races, they would gain a net of eight seats from Democrats, giving them a 53-to-47 majority in the 114th Congress. If Democrats swept instead, they would lose just one seat and would hold a 54-to-46 majority. Considering the uncertainty in the landscape, estimates from betting markets that Democrats have about a 63 percent chance of holding their majority appear to be roughly reasonable.
Enten focuses on the House:
Since 1866 only thrice (1934, 1998, 2002) has the president’s party not lost seats in a midterm. In all three of those elections, they gained fewer than 10 seats, which isn’t even close to the 17 seats Democrats need to take the House today. The GOP will probably maintain control come 2014, but there still seems to be some misunderstanding about what type of national wave it would take for Democrats to take back the House. The Democrats currently have a 5pt lead in the HuffPollster national House ballot aggregate. If it holds through 2014, the Democrats would be in good shape to win a majority in the House.
He later bets “that the national environment for the 2014 midterm elections will turn against Democrats enough to keep them from winning the House.”