There are 8 million people who are getting health insurance through the exchanges now. This number will continue to grow throughout the year as people experience "life events" that allow them to sign up for the exchanges after the end of the open enrollment period. (Life events include losing insurance due to job loss, a death in the family, and divorce. Job loss is the most common item in this group with close to 4 million workers changing jobs every month.)
The fact that the exchanges are now up and running means that millions of people will have direct knowledge of Obamacare rather than just hearing the media and politicians talk about it. While this direct knowledge is likely to influence their view of the program, this possibility is never taken into consideration in the discussion of public attitudes toward Obamacare in the Post's "The Fix" column.
It is likely that many people would be opposed to the idea of a government-run insurance program that pays for most of the health care costs of people over age 65. However, Medicare is a hugely popular program even among Tea Party conservatives. People's direct experience with Obamacare will likely have more impact on their attitudes toward the program than what they are being told about the program by the media.