The phrase "Democrat voters" has been used by the AP, Reuters and USA Today, among others. That's the first time media outlets have consistently made the same mistakes, right?
It is perfectly proper to do so.
No, no it isn't. Also, you'll note that Democrats themselves never do it. Why do you think that is?
Unlike the party, individual voters are never referred to as "Democratics".
Wow, did you ever study English? An individual voter is a noun, and therefore is a Democrat. Again, "Democratic" is an
adjective.