The "people who did it" here was a Buffalo's TV station website. It's not uncommon to see newspapers or news websites use Democrat as an adjective, particularly when referring to voters, not the Democratic Party itself. This is especially true in headlines, or in other cases where space is at a premium.
Democrats have no inherent right to tell the rest of us what words we can use.
It's so hilarious that grammar is a political issue with some. Everything is not a huge political drama. You can use whatever you want, but that doesn't make it grammatically correct.
