The trouble is that Democrats do tend to attract the extreme left. And the extreme left is indeed Anti-American and sympathetic to America's enemies.
I grant that you can find some on the extreme left that believe as you say. But my personal experience, living in a blue area, is that those are the exception rather than the rule.
It's easy to have a chuckle and demonize those we disagree with. It's harder to find common ground about what makes us American. But, if my personal experience is an indication, it's not very hard.
Som are, I'll grant you that.
I live in a blue area. I have to work with these people. They're not that different. They are not the caricature of an America-hating extremist.