If by emotional instability you mean, McCain has a bad temper, I agree. If you mean McCain is insane or crazy, I disagree. I have problems with McCain based on his support for CFR and liberal immigration reform that promotes amnesty. I also didn't like his torture amendment in the last defense appropriations bill. OTOH, Bush signed off on CFR and McCain's torture amnedment. Bush and McCain also agree on liberal immigration reform policy.
That'd be it...but he can't control it; that's the big problem - I do NOT want him to move beyond the senate.
I'm sitting out the California gubernatorial race, because I cannot punch the chad for Arnold - all is lost in this state, anyhow........but I really would have to think about a theoretical McCain versus Kerry or Gore (Hillary won't be the nominee - bookmark it), and probably hold my nose while I voted.
Bottom line: McCain is not presidential material.