“America First” is a rather broad concept and a good slogan, so it’s only natural it’s been used before.
I think people by and large are ignorant of history. So I’m not sure if this is much of a controversy. Does Joe Voter know about the past use of the phrase? I doubt it. Would he care if he did know, or did he hear about it on the news and decide it matters to him? I wouldn’t imagine so.
It’s a good phrase to reclaim from past abuse, must it remain forever tainted?
Unfortunately, very true in general, disregarding for the sake of discussion the "America First" phrase. The dumbing down of education for four decades has resulted in an American electorate more prone to appeals by candidates based more on primitive emotion and instinct rather than reason. Politics in the media is treated more like an entertainment event, rather than the serious business of helping the public to decide rationally what kind of government we're going to have.
Am intellect named George Santayana said about 100 years ago, "those who ignore history are doomed to repeat it." Well, if the masses are ignorant of history (and the dumbing down of American society guarantees that ignorance is pervasive), that means the society is doomed!