Yes but it's actually very easy to get a SECRET Clearance, although a TOP SECRET is a very different thing.
All they do initially with a SECRET is basicly run a National Agency Check which will turn up convictions, not arrests, associations with anti-whatever radical groups, all the big watch lists like the FBI's most wanted. They will check with the Credit Agencies, Experion, etc.. to see if you have money problems and would be susceptible to bribes and such. And they check the references you provide, perhaps your last jobs, and a few more things but that's about it. It doesn't even have to be complete before they issue an Interim Clearance which allows you to go to work and gain access awaiting final adjudication of the Investigation.
On top of this USIS(The company that did his investigation), has come under fire saying they were taking short cuts in order to complete investigations quicker and cheaper so that they could pocket more profit and look better to the government who selects contract winners.
Of course this was the same Company who investigated Edward Snowden for his Clearance.
