While the 44th president was good-humoured, cooly intellectual and never less than statesmanlike, his successor is crass, petulant and deeply, deeply insecure.
Rarely was that contrast been more nakedly apparent than on 11 September 2019, the 18-year anniversary of the terror attack that shook the world.
When the two Boeing 767 jets hijacked by al-Qaeda operatives slammed into the twin towers of the World Trade Centre on that fateful day in 2001, 2,606 people died on the streets of New York City in addition to the 157 aboard the two planes, a day of unspeakable horror that led to more bloodshed in George W Bush's retaliatory War on Terror, which the US has still not disentangled itself from.
In 2019, Obama remembered the occasion by praising the "spirit of unity and togetherness" the tragedy had inspired among Americans who lived through it.
Trump too began the day with an appropriately solemn and respectful tribute...
...only to then revert within moments, unbelievably, to his usual gripes about the chairman of the Federal Reserve, Jerome Powell – who he appointed – being "a bonehead" for not lowering interest rates.
He also found time to obsess over his negative poll numbers before trudging off to the Pentagon in Arlington, Virginia, to read out scripted remarks he presumably had a little hand in writing or sincere emotional investment in delivering.