I agree - but I can understand the motivation.
If you want to make a point and demonstrate the vapid shallowness of the current Democrat Presidential candidate - its easier to contrast him against a Dem icon, without pointing out that said icon was also very flawed....(because then you have to start laying out fairly lengthy records and explanations -- and you quickly lose the audience). I think Rush made the point he intended to make.
Good point. Repubs often point toward JFK and even more often toward FDR in order to make a point. Not because these are good presidents but because Dems believe they were good presidents, so they serve to make a point.
As you say, they are icons in the Dem world.