Edit: thanks to currymj below for the link to https://en.m.wikipedia.org/wiki/Democrat_Party_(epithet)
Democrat: A supporter of democracy; an advocate of democratic politics.
One adjective for persons another for process. In some cases both would be correct but the meaning will differ.
https://en.wiktionary.org/wiki/democrat https://en.wiktionary.org/wiki/democratic
Good, that's consistent with my French and Greek, sorry for checking but your comment really surprised me ! Didn't realize it was a joke until having already checked...
This doesn't seem to be widely supported.
Vox.com (a left-leading outlet) uses "Democrat voters" frequently, eg:
"...while 82 percent of Democrat voters named the pandemic the top issue.."
https://www.vox.com/2020/11/4/21548770/exit-polls-election-t...
Democrats themselves don’t seem to think about it much but there is a portion of conservative media that is very careful to always say “Democrat party”.
see here: https://en.m.wikipedia.org/wiki/Democrat_Party_(epithet)