Just something MAGA-people seem to have a hard time with sometimes. Probably not as much when Americans are speaking to themselves, but as a non-American, sometimes it’s challenging to get “those people” to admit that there is indeed anything wrong with the US. As in they won’t accept a single criticism, and will loudly proclaim “America is the greatest country in the world”, while wearing a “Make America Great Again” hat, which for me pretty explicitly means America isn’t great, if it has to be made to be such again.
(Paraphrasing an old comment from the Bad Site)
“Make America Great” would be a fine, if bland slogan. Everybody wants that. It’s not controversial, but also not distinctive in any way.
“Make America Greater than Ever” would be better. The implication being that we can do better, and be better. But they intentionally went with something else.
It seems to me, and as you have identified, that the “Again” is the key part of the phrase that drives the whole narrative. Here’s the kicker: by nearly every objective measure, the country is safer, richer, more equal, and has a better overall quality of life today than at any point in history[1]. The only thing that has significantly declined over the last 40-50 years is “the percentage of total societal influence held by straight white men.”
“Again” is the dog-whistle of misogyny, racism, and homophobia, wrapped up in the plausible deniability of nostalgia for an objectively worse time.
[1] There may be some room for disagreements here, primarily because of the first Trump administration and the pandemic years causing some backsliding, but this was especially true in 2016 when the slogan first really appeared, which is when it should be judged.