Why are democrats portrayed as communist and republicans as fascist?

cause thats what peoples say

i dont think people always see them that way

Because of the political spectrum and where Democrats and Republicans fall relative to one another and relative to America's center on the political spectrum.  Democrats are left of America's center on the political spectrum. Republicans are right of America's center on the political spectrum: Democrats left-wing; Republicans, right-wing.

On the political spectrum, the type of government that is farthest left is communist and the type of government that is farthest right is fascist. This is common knowledge found in any high school political science textbook.

So when Republicans portray Democrats as communists, they are accusing them of being political extremists, the absolutely most extreme one can be as left-wing extremists, short of being an anarchist, anarchy being an accusation they would level if not for politics being about government and if not for Republicans finding fault with Democrats' government agenda that they see as antithetically different than Republicans', thus making an accusation of anarchy not make sense since anarchy is no government and that would make Democrats' agenda no government at all rather than antithetically different government. And when Democrats portray Republicans as fascists, they are accusing them of being political extremists, the absolutely most extreme one can be as right-wing extremists.

This name-calling is then underscored by highly prejudicial associations since America's two worst enemies, America's two largest existential threats, over the past century or ever really have been communist USSR in the Cold War and fascist Nazi Germany in World War II. So, this name-calling carries a lot of baggage and is meant to imbue each as a sworn enemy of the United States, an enemy so terrible as to be a threat to the ongoing existence of the United States.

Because fearmongering works.

Because people don’t really know much about either of them in North America.