This is one of those people Peggy Noonan describes as "a ungrateful liberal thoughtlessly enjoying freedoms won by greater men of courage".
I bet he thought Klinton had a mandate even without ever winning 50%. And I do believe Bush crossed the %51, so his numbers are wrong anyway.
The last Democrat before Carter to get more than 50% of the popular vote was LBJ in 1964. The last Democrat before LBJ was FDR. Before FDR you have to go back to Samuel Tilden in 1876 (who lost the electoral vote to Rutherford Hayes). The last Democrat before FDR who was elected with more than 50% of the vote was Andrew Jackson in 1828.
These and other fun facts can be found in the Atlas of U.S. Presidential Elections.