"Donald Trump is not a uniter. Donald Trump is a divider."
Obama is a total divider, the most divisive US president I've ever witnessed.
All through his term, he has been pretty much deliberately seeking ways to turn American citizens against each other along economic (Regularly demonizing the rich, openly cheering on Occupy Wall Street), religious (Ending the celebration of National Day of Prayer, which had been observed by the President each year for over 60 years and whose roots go all the way back to George Washington, and constantly trying to find new ways to give the finger to Christians and Jews while simultaneously kissing up to Muslims in every way he can), racial ("If I had a son, he'd look like Trayvon Martin,"), and ESPECIALLY political lines (i.e. He once gave a speech in which he identified various GOP fundraisers and benefactors by name and openly accused them of "Betting against America").
Let's not also forget that when he announced his planned executive order to give blanket amnesty to millions of illegal immigrants, he gave a speech in which he openly accused those who opposed it of racism/ xenophobia.
For a president billed as "The Great Unifier," Obama has left America more divided than ever. I'd say that's a big part of what his legacy will be.