Is it normal to believe in the american "monoparty"
This doesn't apply to citizens who vote Republican or Democrat, this only applies to politicians in D.C.
Look at the behavior of Republicans and Democrats in Washington: it's obvious they both want the same thing, but for the sake of keeping up appearances, Republican politicians have agreed to be the "bad guys" who always take the blame, always take the fall, and never, EVER fail to cave any time they face even the tiniest amount of pressure from the left
There's only one party in Washington, and the only difference voting makes is if you want people to suck you off for being an open-minded hero of the disenfranchised or to physically assault you for being a racist, sexist, homophobic, transphobic, etc. etc. etc.