German Lopez at Vox says:

A new RAND Corporation survey estimates 9.3 million Americans gained insurance between September, the month before Obamacare's marketplaces kicked off, and mid-March. That represents a drop in the uninsured rate from 20.5 percent to 15.8 percent, according to RAND.

The report doesn't necessarily translate to a huge victory for Obamacare's marketplaces: among the newly-insured, the biggest gains were in employer-sponsored coverage.

Republicans right now appear to be preparing to run for midterms on a strict anti-Obamacare platform. That could be a mistake.