The emerging consensus on the first months of the Affordable Care Act is that while the implementation of the exchanges has gone poorly by any reasonable standard, and that while cancelations of individual insurance policies have greatly exceeded expectations, the Medicaid expansion has been fairly successful, considering that a large numbers of states have refused to participate in it. But Sean Trende gives reason to doubt this consensus view. The Obama administration has observed that as many as 4 million people have signed up for Medicaid coverage in recent months, a success they’ve attributed to Obamacare. Trende suggests that most of the Medicaid enrollment we’ve seen would have occurred even in the absence of the new health law, in part because a large share of new Medicaid enrollees are in states that chose not to accept the Medicaid expansion, but also because the expansion states tend to be states that already had relatively expansive Medicaid eligibility. By comparing Medicaid enrollment across states before and after the ACA entered the picture, Trende estimates the impact of the expansion. Of the 4 million new Medicaid sign-ups, he (tentatively) suggests that only 380,000 are directly attributable to the Obamacare Medicaid expansion.