To be fair, Republicans will give "their guy" a pass on something they'd crap their pants over if a Democrat did the same thing. There are almost too many examples of that with conservatives ragging on Obama for doing the things the Bushes and Reagan did with which they had no problems.
As for being a democrat being a mental disorder, there's actually a book titled "Liberalism is a Mental Disorder." Unfortunately, it was written by a conservative with a mental disorder (radio talk show host Michael Savage), and wrote the book from basically the point of view of, "If you're not conservative and you don't think like me, you have a mental disorder," which is pretty much how many conservatives think. There is a less impassioned, less agendized book that just lays out the facts called "The Liberal Mind: The Psychological Causes of Political Madness," written by Dr Lyle Rossiter, a clinical psychologist. Still, and unfortunately, while his book is dryer and less agendized, his book does come at you from the point of view of, “My political views are so obviously correct that anyone who doesn’t accept them must be mentally ill."
Rather than an "I'm right and you're wrong" agenda take on liberalism and conservatism, I prefer to just step back and take a look at it objectively. My take on it is...
There is a group of people who want instant gratification. They have short attention spans and get bored easily, but when they want something they can only think about that one thing and are usually adamant about getting it, even if it requires a temper tantrum to get it. When they want something, the fact that they want it is justification enough for them to think they should have it, and the more badly they want it the more justification there is in them getting it. They are dependent on adults and other more mature people for their every need. They want and need to be fed and clothed by others. They have no responsibilities, nor do they understand the concept of responsibility. Anything bad that happens to them is always someone else's fault, and they blame others accordingly.
This group of people is called, of course, children. It is interesting that they have so much in common with liberals. Is that a mental disorder? I think the answer to that is more political than medical, but the similarities and commonalities between children and liberals are there, objectively, nonetheless, and they cannot be refuted.