To narrow your search results, type in your topic as a keyword search in the 1st box (default setting). Then combine it with an assigned Library of Congress subject. tag in the second box (select "subject" using the drop-down "All Fields" arrow).
Examples of a few precise Library of Congress subject tags (headings):
You can also try subject searching using the word "Policy" combined with a specific area, such as:
If you find the results to be too global, then add the words "United States" to your search and see if that helps.