Mitt Romney appeared on CNBC for a Larry Kudlow interview:

This is both the best and the worst of the GOP front-runner. On jobs, energy and taxes he was strong and informed. (He should, however, stop saying he spent his ”whole life in the private sector.” It’s not true and erodes his credibility for no good reason.) He even managed to sound a bit populist on his support for middle-class tax relief. (He said he wasn’t interested in lowering taxes on the top 1 percent of taxpayers.) On free trade he was candid about the Chinese, suggesting a closer trade relationship should be offered to those who respect our intellectual property and don’t engage in unfair tactics.

But on the Bush tax-cut extension, Romney didn’t have a good response for his opposition to the deal last December. Kudlow grilled him on why he didn’t back a two-year extension. “The good should never be the enemy of the perfect,” lectured Kudlow. Romney insisted the Republicans should have gotten a permanent deal. (This, of course, was never in the cards.)

But he ran into trouble, again, on distinguishing RomneyCare from ObamaCare. On his health-care plan he said, “It wasn’t perfect,” but he ignored Kudlow’s question as to whether the individual mandate was a mistake. He repeated his latest talking point on RomneyCare: “I’m very happy that the Democrats are celebrating the fact that we put in a health-care proposal in Massachusetts as an experiment. And I have one question for them — why didn’t any one of them or the president ever call me and say: ‘What worked?’ ‘What didn’t’?”

But this is a problematic defense. I e-mailed a Romney spokeswoman, asking “What worked and what didn’t in Massachusetts? Does he think [MIT professor and adviser Jonathan] Gruber didn’t give the White House an accurate picture of the Commonwealth plan?” She replied “Gov. Romney wrote about healthcare extensively in his book and I think a lot of the answers to your questions will be in there.”

But they aren’t there. In his chapter, “Healing Health Care” he writes favorably of the individual mandate as a means of eliminating the “free rider” problem (p. 173). He writes in glowing terms about his partnership with the late Sen. Ted Kennedy (p. 174). And he raves that his plan has been a huge success (pp.175-179). But where is the part about what didn’t work? The self-critique appears on p. 175, when he criticizes the legislature for adding costly items. He observes, “Even the best written legislation is subject to rule-making and interpretation by political appointees, and it can be adjusted by subsequent administrations; their predisposition to grow or restrain spending has a major impact on cost.” Yet he passed a bill that was an invitation for liberal add-ons in one of the bluest states in the country.

Romney, as the campaign goes on, will be closely questioned about all of this. It’s not enough to have a snappy line (the “He didn’t call me!” remark sounds a little whiny). He eventually will have to decide whether to defend or reject his individual mandate. Thinking he can get through a whole campaign without confronting that issue is as self-deluded, well, as imagining a health-care system of state subsidies and mandates wouldn’t lead to runaway costs in Massachusetts.