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President Obama just delivered the most convincing argument for why Donald Trump can’t be president.

It’s hard to think of a more perfect opener for Obama’s speech than Sharon Belkofer, the self-described “little old lady” from Ohio, who got up and did something no one did for Donald Trump at last week’s RNC: She testified to Obama’s character based on personal experience.

And then, the video. The video, without ever acknowledging Trump, made the most convincing case we have seen this convention for why Donald Trump cannot become president. It argued that the presidency is the most difficult and serious and crushingly lonely position in the world, and that it takes someone of exceptional moral character to occupy it.

Obama’s speech built on this foundation. It sounded, in some ways, like he was running for a third term. He opened by reminding the country of the job that he was given—specifically resuscitating the economy, which was in the toilet—and how far we’ve come since then. It was a greatest hits of the Obama era: economic recovery, the killing of Osama bin Laden, marriage equality, health care.

Obama walked a line between recounting all that he’s achieved in the last eight years and reminding the country of the work that still has to be done. It was a speech in which the baton was passed. The only way to continue—not just preserve or maintain, but continue—the progressive agenda he set out to accomplish is to elect Hillary Clinton president.

It was no accident that he called back to Bill Clinton’s famous line from his first inaugural address: “There is nothing wrong in America that can’t be fixed with what is right in America.” Obama continually leaned on this refrain, subtly contrasting his optimism in the country’s future with the millenarian fever dreams presented in Cleveland last week.

But mostly this was a speech about how being president is a job, and a really hard job at that. It’s a job that requires a sturdy character, a willingness to take on thankless tasks and unthinkable challenges, and a well of empathy. Obama did a decent job of arguing that Clinton was this person, but he was best when arguing that Donald Trump absolutely isn’t that person.

He dragged Trump. “Don’t boo, vote,” will almost certainly be the line most remembered from this speech, but he demolished Trump directly and indirectly by returning again and again to the fact that being president is work. This was a speech about the responsibility of being president, and he made it abundantly clear that it’s a responsibility that Donald Trump cannot handle.