Sebelius noted that the administration has made unilateral changes in implementation. Republicans are well aware of that. But in terms of proposing legislation to fix or improve the president’s landmark achievement, Democrats have offered next to nothing.

What changes could they advocate? Most likely they can’t suggest anything really big, like repealing the individual mandate; most Democrats would see that as gutting the law, and any candidate who advocated it could risk party support. But perhaps Democrats could, as the blogger Mickey Kaus suggested, propose cutting back on mandated benefits like mental health treatment and pediatric dentistry, in the hope of bringing down premiums.

“Would [that] require Democrats to in effect admit error — that they ‘went too far’ in building out Obamacare?” Kaus wrote. “Well, duh! Voters tend to like admissions of error, especially if they seem likely to lead to better policies in the future.”

It’s an open question whether voters would really welcome Democratic confessions of error in creating Obamacare. Most Democratic candidates probably don’t want to learn the answer.