Let's see how much I can correctly guesstimate based on GameFAQs topics and American media.
Party the first president belonged to.
The Democrats. A long time ago the Democrats were the conservative ones and were all for government control and stuff, while the Republicans were liberal and fought for free market, freedom of speech, and gender equality. But something happened (probably involving sending Hugh Jackman back in time) that their 'alignment' swapped. George Washington was the first president and would probably be all for state power and stuff (after the hard-won liberty) ergo he was a Democrat.