According to the Pennsylvania GOP, by way of John L. Micek by way of the Pittsburgh Post-Gazette. So why did they suggest such a thing, in the ad above:

"I think we were obviously trying to get some attention to this important race,'' said Michael Barley, spokesman for the state Republicans.

Oh, so you were trying to get attention for an election by comparing the president to the murdering thugs who ran the Soviet gulags. Well, why didn't you say so? I guess it's all OK, then. Next there going to tell us there wasn't really a boy in that balloon, after all.