Yesterday at the hearing with Sally Yates, Republican Senators were fixated on the idea of leaks. Just a note--that Michael Flynn was only fired when the Washington Post published a story that had been leaked.
I would suggest that leaks came from the Trump White House--not the former Obama administration. In the transition period, normal Republican national security types had to interface with the Trumpsters. They found that transition people requested classified documents and put them at the SCIF (The term coming from this investigation for a place where classified documents are read.) What they found was that Trump people were xeroxing these documents and taking them to unsecured places and circulating them to people without security clearances.
These people have seen White House staff disregard the rules and have been leaking about it. So the Republicans should look at their old colleagues who were so offended by this administration as the source of the leaked stories.