And note that all mainstream Democrats distanced themselves from this ad and from any connection to it.
While the Bush / Hitler comparisons are over the top (I'd personally think of Bush / Cheney more in the Mussolini-lite mode, though not quite as competent as Il Duce), there was the war of aggression, wiretapping, torture, illegal detentions, blocking "dissidents" from attending their public rallies, and the exploitation of people's fear for political gain. Even a Republican should have felt uneasy at what was going on.
Compare this to... basically wanting to expand Medicare / Medicaid to all Americans. Which is bringing out the Republican / Conservative pundits in droves to make the Hitler comparisons and express their paranoid fears of death panels. And from their political leaders, there's not an ounce of serious pushback on this rhetoric. Some are actually encouraging people to think this way.
The Republicans are either silent or actively encouraging the crazies. The Democrats, both in and out of power, have done everything they can to run away from the crazies on their side. There's no equivalence here.