Here's why Republicans won't be able to get any traction on their effort to claim John Roberts turned Obamacare into the biggest tax increase in American history:

Romney himself has made a forceful case for the value of imposing a tax penalty on consumers who choose not to buy health insurance -- explicitly describing the penalties associated with a health care mandate in terms of taxation.

Specifically, this is what Romney said:

Right now people who can afford to buy insurance make the decision, ‘I’m not going to buy insurance. I’m going to be a free rider.’ And if I get sick or get in a serious accident, then government’s going to pay for me. That, in my view is the big-government solution we have right now. The alternative – there are a couple of alternatives – one is to say to employers you must give insurance to every one of your employees. I said, ‘No, I don’t want to do that. That’s going to kill jobs.’ And the other alternative is to say to people if you can afford to get insurance, you ought to buy insurance. And if you don’t buy it you’re going to get penalized with a higher tax rate for not having gotten insurance. Now you tell me which of those is the big-government plan and which is the personal responsibility plan.

The one and only intellectually consistent argument Romney could make against Obamacare is that the difference between Romneycare and Obamacare is that Obamacare was unconstitutional ... but he can't make that argument any more. Deriding it as a tax on everybody or tax penalty on free riders won't work because (a) it's not a tax on everybody and (b) imposing a tax penalty on free riders was his idea.