Using "Democrat" as an adjective

[andyfox]

"voters respond more negatively to 'Democrat' than 'Democratic'

No doubt. Democratic can be confused with democratic, and we all like democracy. But Democrat had the same feel as bureaucrat.

[roueful]

The example in the op isn't an adjective, it's still a noun. "Democrat President" is a compound noun phrase, like 'the Africa report' or 'the poker site'.