It can be difficult to search on a topic or concept that is known by more than one name. Researching the Affordable Care Act, can you search on "Obamacare"? Do you need the full name of the act, Patient Protection and Affordable Care Act? What about ACA? Or PPACA?
Recommendation: use your initial search and the resulting articles to seek out the most accurate subject headings.
Here's an initial keyword search for Affordable Care Act:
This search produces many results, all of which use some or all of those terms ("affordable," "care," and "act"), but not necessarily in the context of the specific legislation. Find an article that does refer to the specific legislation and view the subject terms on that article.
Click on that hyperlinked subject term to redirect your search towards all articles which mention PPACA specifically. It will rerun your search and bring more relevant results.