How was the affordable care act of 2010 (aka obamacare) an example of federalism at work?

Please write in your own words: 

this what I have found.
Powerful interests (conservatives in some states who oppose the Affordable Care Act) are able to prevent a less-powerful group (low-income people who make up a larger portion of the population) from being able to take advantage of either Medicaid or subsidized health insurance. So, in this case, rather than protecting the interests of the people, federalism enables some people to deny access to health care for others.

Hope this helps.