There are a number of things that have been great about the United States of America:
Social Security is great!
Medicare and Medicaid are great!
Having more people with affordable access to healthcare as opposed to fewer people is great!
A safety net for the poor is great!
Good public education for all is great!
Having excellent colleges and universities is great!
The Civil Rights Act is great!
The Voting Rights Act is great!
The American with Disabilities Act is great!
The Environmental Protection Agency is great!
The Clean Air Act is great!
The Clean Water Act is great!
A Clean Power Plan to protect a livable climate is great!
National Parks and National Monuments safe from corporate exploitation are great!
The Emoluments Clause of the U.S. Constitution is great!
Having strong democratic allies around the world is great!
Caring about international human rights is great!
Standing up for journalists and a free press is great!
Not having a president who believes the press is the enemy of the people is great!
Not having a president who lies relentlessly to the American people is great!
Not having a president who is under six separate investigations is great!
Not having a president who has better relationships with murderous dictators than with our long time democratic allies is great!
Accepting refugees escaping violence and oppression is great!
Not separating children from their parents is great!
Not putting children in detention camps is great!
Not discriminating against people who orient themselves to religion differently, persons of color, persons who are LGBTQIA, and women is great!
As a country, we have fallen short of the Beloved Community, we have not implemented all of these great things fully, and sometimes we have fallen very short of the ideals and values that we have aspired to express, but we have still managed to do some great things together as a nation. (Yes, we have also done some really horrific things as well – genocide of indigenous people, slavery, Jim Crow, perpetuating the inequality of women, some clearly unjust wars, and we are an incredibly violent and often unjust society. There is nothing great or good about these things.)
It does not appear Trumpian Republicans are really trying to make America Great Again. Rather it seems they are trying to systematically destroy many of the greatest things we have accomplished. If you ruin all of these great things, what is left that is really great or good about our common life together? At the very least the result is a diminishing of whatever greatness we may have rather than its enhancement, and that is anything but great.