I was not aware of this; I watched to whole committee hearing last night and never heard him questioned about these donations.
I saw the below piece this morning, it blew me away.
excerpt:
“According to the Washington Free Beacon, Koskinen has donated about $100,000 to Democrat candidates and committees since his first donation in 1979. His donor recipients include Gary Hart, the Democratic National Committee, the Democratic nominee in each presidential campaign since 1980 (which would even include Walter Mondale, who stood no chance of beating President Ronald Reagan in 1984), the Democratic Congressional Campaign Committee, and Hillary Clintons and Barack Obamas campaigns. He most recently donated $2,500 to Sen. Mark Warner (D-VA) in 2013.”
http://pjmedia.com/tatler/2014/06/23/irs-chief-koskinen-has-donated-big-to-democrats-over-the-years/