Polls suggest that more and more, opposition to Obamacare is based on voters' personal experience, and not just on what they have heard or read about the law.

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.

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.

'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.'

So Republican candidates bash Obamacare and move up in the polls. Given that public opinion remains firmly against the health care law - as it has been for years - that's not a shock. Democratic beliefs to the contrary are probably wishful thinking.

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.

A remarkably revealing portrait.