What does “Bartlett’s Best” mean?
Solution 1:
It's a reference to Bartlett's Familiar Quotations, the classic collection of quotable quotes. It was first published in the mid-1800s, and has been pretty much continuously in print ever since. Before there was the internet, if you needed a pithy epigraph or wanted to know "who said that" you turned to Bartlett's.
The implication of the line here is that the things Trump says are so unintelligible that George W. Bush's previously-ridiculed utterances sound brilliantly quotable in comparison.