If the popular vote is an indication, he has a smaller percentage of popular support than any other president has had.
Well, as long as one ignores Grover Cleveland (2nd term), James Buchanan, Richard Nixon, Bill Clinton, Woodrow Wilson, Abraham Lincoln, and John Quincy Adams...
I was referring to the number of more popular votes that the losing presidential candidate received.
Hayes defeated Tilden 185 to 184 electoral college votes but 254,000 fewer popular votes.
Harrison defeated Cleveland 233 to 168 electoral college, but 91,000 fewer popular votes.
Bush defeated Gore 271 to 266 electoral college, but 500,000 fewer popular votes.
Trump defeated Clinton 304 to 227 electoral college, but 2.8 million fewer popular votes.
The popular vote difference with Trump's victory is far greater than any other time in American history.