this is true if the slogan was make america great. but its make america great "again" that implies the history and the future potential of it happening again
I don't think the presence of "again" contradicts anything I said. At the very least you're conceding that, within "MAGA," the greatness of America is something that changes with time.
So what matters doesn't seem to be whether a party "loves" America or not, because sometimes they love it and sometimes they don't. What matters would seem to be the particular aspects of America that the party loves.
"Make America Great Again" has always been pretty vague about the precise time in our history that it hearkens back to. Trump promises a return to greatness without directly telling us when that period of greatness was. This lets people fill in the blanks, and the vagueness really lends itself to idealizing a time when power was concentrated in "white America." So when you read about a "love letter" to America in times like these, you really gotta wonder what values are being praised.