This was published as a Wall Street Journal Think Tank column on August 21, 2014.

Democrats generally are not campaigning on the Affordable Care Act, but in a new campaign ad Arkansas Sen. Mark Pryor does just that.

Some have commented on the fact that Mr. Pryor does not mention the ACA by name in the ad, referring to it as “a law he helped pass.” Just as interesting is the part of the law the ad features: its protections for people with pre-existing medical conditions. With all of the focus on the ACA’s rollout problems last fall and the ACA’s coverage expansion, we have not heard much about “pre-x” in some time, but in many respects it’s the mega benefit in the law.

According to our Kaiser Family Foundation July tracking poll, 53% of Americans have someone in their family with a pre-existing medical condition. Not everyone with a pre-existing condition had a problem getting health insurance before the ACA went into effect, but many did and even more worried about it, and everyone with a pre-existing condition – roughly half the population – benefits from the pre-x provision in the law in terms of gaining greater peace of mind that they are guaranteed access to coverage if they lose insurance or change jobs.

Pre-x is also one of the most popular provisions in the ACA and popular on a bipartisan basis. While 70% of Americans support it, 69% of Republicans do, too. No doubt Sen. Pryor, who is locked in a tough race against Republican challenger Rep. Tom Cotton, had this in mind when he resuscitated pre-x to feature in his ad.

Pre-x, of course, is not cost free. Premiums have risen for some to help pay for covering people who are sick.

Sen. Pryor’s willingness to campaign on an element of the ACA may indicate that the law is declining as a political weapon for Republicans and even gaining some traction for Democrats in some races. But his selection of the pre-existing condition provision as the element of the law to campaign on brings back to prominence the somewhat forgotten element of the law that benefits the most people and, in sharp contrast to the ACA overall, is popular on a bipartisan basis.