Given that making an argument on the merits that there is an “imperial presidency” on domestic as well as foreign policy is essentially impossible, as you can see from these comment threads the preferred response has been to say that before Obama was elected nobody thought that the president was subordinate to Congress on domestic policy, so QED it’s just an excuse being made by Obamabots.
As Adam points out, however, is that it just isn’t true. In my case, I was apparently making excuses for the Obama administration well before the Iowa caucuses, and was even prescient enough to apologize for him before he had announced he was running. And, in general, the fact that evaluating the presidency as if the U.S. has a parliamentary system is a fairly common fallacy, it’s not a common fallacy among political scientists. Look at any work on the presidency, from a decent undergraduate textbook to a scholarly monograph, and I defy you to find a single example of someone who thinks the presidency dominates domestic policy. That there is a consensus or near-consensus among actual scholars in the field does not in itself prove that the argument is right — although I think it quite obviously is — but to say that it was newly invented to defend Obama is just 100% pure ignorance.