Part of him didnt want to let go. Another four years would have been seducing, were it allowed. But that, he knows, would be proof of failure. Before a thunder mob, an emotional Barack Obama reminded Americans why he is a once-in-a-generation figure, constructed the lawsuit for his successor and warned that Donald Trump threatens the 240 -year-old fabric of American democracy. It was an elegiac piece of political theater that contrasted with last weeks Republican convention in which a bellicose Trump, ranting in front of his own giant image, bordered on fascist irony. Obama had worked through six drafts of the speech and remained up until 3.30 am rewriting it. He reportedly dismissed the idea of a valediction like those delivered by Ronald Reagan in 1988 or Bill Clinton in 2000, saying he wanted it to be about Hillary Clinton. And it was, dutifully yet artfully, about Clinton, including a warm hug at the end when the beaming candidate herself arrived on stage. And yet it was also, inescapably, a long goodbye. Four more years! came the occasional exclaim from delegates in the audience. As Obama, the son of a Kenyan, told the African Union last year, if he was constitutionally able to run again, he would have a decent shooting. But, he also pointed out, any leader who believes they are indispensable has failed to build their nation. Which brought him, on Wednesday, to Donald Trump and his slogan promising to make America great again. Obama told: America is already great. America is already strong. And I promise you, our strength, our greatness, does not depend on Donald Trump. In fact, it doesnt depend on any one person. Having witnessed the perils of tyrannies all over the world, Obama delivered a scathing reprimand to Trumps claim, heard down the ages from charismatic leaders, that he alone can fix the countrys broken system. Ronald Reagan called America a glistening city on a mound, he continued. Donald Trump calls it a divided crime scene that merely he can fixing. It doesnt matter to him that illegal immigration and the crime rate are as low as theyve been in decades, because hes not offering any real solutions to those issues. Hes just offering slogans, and hes offering fear. Hes betting that if he frightens enough people, he might score just enough referendums to win this election.