Your search results may be more relevant on the Congress.gov website because the space between two search terms now uses the AND operator instead of the OR operator.
Before June 26, 2017 the space between the two search search terms meant OR, providing many results that may not have been relevant. Red Blue meant Red OR Blue.
Going forward from June 26, 2017, the search terms are joined because the space means AND. In other words, Red Blue means Red AND Blue.
You may still use the OR operator if you need to expand the results.
The Venn Diagram illustrates the two concepts.
When you search Red Blue, you get the darker portion of the Venn Diagram, or the UNION of the two circles. But, if you search Red OR Blue, you get the symmetric difference of the two circles minus the darker portion.
Practical Example as of June 30, 2017
If you search affordable care on Congress.gov, the results set will be 212. But if you search affordable OR care, the results set will be 1,224. The default for a space is AND.