Do they **REALLY** believe that America was "never great"?
Many of them do. Progs are not unique in rejecting something that isn't absolutely perfect. We have seen conservatives right on these forums who will not vote for who they consider the lesser of two evils - they demand a politician who is in complete lockstep with their personal beliefs, and will reject a candidate based on one point of disagreement.
America was never great sounds like the whining of a teenager aching for attention - not the observation of anyone even marginally aware of history.
And there you have it. If you ask a diehard prog about anything historical, they either don't know or they have a highly skewed version that was programmed into them by Leftist teachers and the media. Many of them are Holocaust deniers who think 9/11 was masterminded by Dick Cheney. They don't even know what's happening in this country right now, let alone world events 50 years ago.
The US is a remarkable country in that hundreds of millions of people from all walks of life can live in it and largely get along. The MSM likes to highlight the division and conflict, but any one of us can see for ourselves that that is fringe and isolated, not the norm of day to day life. It's like when there's a school shooting they focus on it and present it as an epidemic, ignoring the 200,000 schools that *didn't* get shot up.
Trump is right that our news media has become the enemy of the People. I have been saying it for decades, and I'm not alone. They hammer it home that the US sucks, traditional values suck, all non-Democrats suck, and absolutely all white people suck, especially if they're men. So if mush minds think America isn't that great and never has been, that's Leftist programming in action, not based on any rational observation.