Why did so many Democrats lose on Tuesday? Here's the simplest answer: President Obama was a political dead weight for his party.
No Democratic Senate candidate performed more than nine percentage points better than Obama’s approval rating in their state’s exit poll. This outlier over-performance was barely good enough for Sens. Mark Warner to pull off reelection in Virginia and Jeanne Shaheen in New Hampshire. (No one thought Warner was in any danger in Virginia. No one.) Notably, both of these candidates are personally popular and serve in states that are evenly split between Democrats and Republicans. They also each spent time as governor before being elected to the Senate.
Outperforming Obama by eight points was not nearly enough for Mark Pryor in Arkansas, who earned just 39 percent support. Democratic candidates in Iowa and Kentucky outperformed Obama’s approval rating by five and six points, only to win 44 and 41 percent support in their respective elections. In Colorado and Georgia, support for Democrats Mark Udall and Michelle Nunn only exceeded Obama’s approval rating by two points, leaving them at 45 percent.
In the four states where Obama held at least 47 percent approval — Maine, Illinois, Michigan and Minnesota — Democrats won three of four Senate races. In Maine, popular Republican incumbent Susan Collins won easily in a race Democrats were less focused on.
The anchor of a president’s approval rating is far from new — presidential job approval has played a big part in predictive models for midterm elections. Indeed, Real Clear Politics analyst Sean Trende performed this very analysis on 2010 and 2012 Senate contests in January. He wrote:
In the 31 competitive Senate races held in 2010 and 2012, the Democratic candidate has run within five points of the president’s job approval in 23 of them (75 percent). Additionally, no Democratic candidate in a competitive race has run more than 10 points ahead of the president’s job approval (or behind it).
It’s possible Obama himself is not the anchor, but his approval is more of an indicator of a state’s basic partisan instincts. But years of midterm election losses have shown that the president's party, and his popularity, are deeply important indicators of chances in midterm elections. This year, the weight of Obama’s standing proved too much for many Democrats.