Q. I'm looking for commentary by the Washington Post on the Supreme Court decision in Citizens United v Federal Election Commission
To find commentary on this case in the Washington Post, start by clicking on the "Journals" tab beside the search box in the middle of the library's home page. Then type "Washington Post" into the search box. After you run the search, choose the Washington Post that has current coverage, better choice is Newspaper Source Plus. Then enter the case in the search box. When I did this I got an extensive list of results.
I think you may have been searching in one of the historical Washington Post databases the first time, and that would explain why you didn't get any hits, since this is a relatively recent case.