Perhaps the most striking thing about the 2015 State of the Union address was not the president at the podium but the audience in the seats. The joint session of Congress listening to President Obama Tuesday night included 83 fewer Democrats than the group that heard Obama's first address in 2009 - 69 fewer Democrats in the House and 14 fewer in the Senate. The scene in the House Chamber was a graphic reminder of the terrible toll the Obama years have taken on Capitol Hill Democrats.

In the end, no single group will mean defeat for the Democrat and victory for the Republican in 2016. But President Obama's troubling legacy - a weakened coalition and growing ranks of alienated white voters - could mean a serious post-presidential hangover for Democrats.

Perhaps the most striking thing about the 2015 State of the Union address was not the president at the podium but the audience in the seats. The joint session of Congress listening to President Obama Tuesday night included 83 fewer Democrats than the group that heard Obama's first address in 2009 - 69 fewer Democrats in the House and 14 fewer in the Senate. The scene in the House Chamber was a graphic reminder of the terrible toll the Obama years have taken on Capitol Hill Democrats.

That does almost nothing to address voters' concerns, which remain a potent factor in the campaign. The bottom line is, there's a reason Republicans keep pushing so hard against Obamacare: So far, it's working.

The Obama damage is two-fold. First, his success relied on a coalition that likely will not survive, or at least survive at full strength, without Obama himself on the ticket. Secondly, Obama drove a significant portion of white voters away from the Democratic Party.

'I haven't used the veto pen very often since I've been in office,' Obama told NPR. 'Now, I suspect there are going to be some times where I've got to pull that pen out. And I'm going to defend gains that we've made in healthcare; I'm going to defend gains that we've made on the environment and clean air and clean water.'

Some Democrats and their advocates in the press believe Obamacare, a year into implementation, is no longer much of a factor in the midterm elections. But no one has told Republican candidates, who are still pounding away at the Affordable Care Act on the stump. And no one has told voters, especially those in states with closely contested Senate races, who regularly place it among the top issues of the campaign.