A few things come to mind.
Holder is impeached and then prosecuted for his crime. A special prosecutor appointed by Congress. Romney's DOJ next year brings charges after Obama and Holder are get kicked out of office. Criminal charges don't end because of an election. Quo Warranto action brought against Holder.
Not to mention the automatic hate crime charge for daring to prosecute Holder.
We all know this is all bogus bunk unless you're a delusional watcher of MSLSD-NBC. I would if I could - not a pansy unlike the rest of the crowd. I guess someone else in power has got balls too - somewhere.
My point is look at the paper trail. The head of the committee had the documents, but refused to do much with them. Issa had to do the end around, which may end up hurting the agents who leaked the information. Not to mention payback to Issa or someone else.
At the end of the day, the question is what is the next step? Issa and Grassley have little to no prosecution powers, and Romney is pretty anti gun himself.