This post has been updated.

Sen. Mark Pryor (D-Ark.) has done something unexpected for a Southern politician enmeshed in a very tough reelection fight: doubled down on his support for the Affordable Care Act.

In an ad released this week, Pryor -- locked in a tight race against Republican Tom Cotton, a conservative, Harvard-educated Army veteran -- affirms his support for Obamacare. Appearing with his father, popular former Sen. David Pryor, Mark Pryor recalls his battle with a rare form of cancer.

"Mark's insurance company didn't want to pay for the the treatment that ultimately saved his life," David Pryor said.

Pryor didn't mention the Affordable Care Act by name. But he did say he helped pass a law that prevents insurance companies from canceling policies when one falls sick.

"No one should be fighting an insurance company while you're fighting for your life," he said.

The senator has spent months attempting to portray himself as an independent-minded politician and distance himself from Washington and Obama, who lost by 23 points in Arkansas in 2012.

So why would he run a spot plugging the president's signature policy achievement?

There's two ways to answer that question.

The long-term answer is that the ACA has long had a branding problem. But specific elements of the law -- the provision that bans insurance companies from rejecting individuals with pre-existing conditions, for instance, or the one that allows young people under age 26 to remain on their parents' insurance, or the one Pryor's ad points to -- have always polled well, even when "Obamacare" didn't.

Then there's this year's summer surprise: the fact that the trail dynamic around Obamacare isn't quite shaping up the way many observers quite expected.

It may not be an unalloyed benefit for Democrats to name-drop the law. But critics aren't necessarily seeing the response they'd expected to attacks -- and are slimming their anti-ACA ad budgets accordingly.

Those spots haven't disappeared -- and "Obamacare" still isn't winning any popularity contests. Justin Barasky, a spokesman for the Democratic Senatorial Campaign Committee, wouldn't even say whether the ad was about Obamacare.

"The ad features Mark's father and is about Mark telling his personal story…his personal experiences battling cancer and fighting the insurance companies," Barasky said in an email. 

Republicans said the spot had no larger significance. “The entirety of ObamaCare remains EXTREMELY unpopular (in fact every single available poll shows that ObamaCare is just as unpopular today as it was in 2010, if not more so)," Brook Hougesen, press secretary for the Republican Senatorial Committee, said in an email.

But the evolving ad strategies on both sides still suggest a shift in perception that's left both parties adjusting their approaches. And that's left an opening for Democrats like Pryor to talk about Obamacare -- even if they never actually mention it by name.