He argued the election presents a choice not between competing partisan visions but between the most qualified candidate in history and one who threatens our system of government itself. In passing Clinton the baton — a gesture made manifest when the Democratic nominee turned up on stage after the speech and embraced the president — Obama launched his first sustained assault on the Republican nominee.

Trump, the president said, is “not really a plans guy. He’s not really a facts guy, either. He calls himself a business guy, which is true, but I have to say, I know plenty of businessmen and women who’ve achieved success without leaving a trail of lawsuits, and unpaid workers, and people feeling like they got cheated.” And Obama paired those street fight-worthy taunts with a soaring panegyric to America’s promise, declaring himself renewed in his faith in the nation’s democracy despite the sometimes grinding frustrations of office and the troubled political season now unfolding.

Whatever you thought of the speech, it made for a heady and riveting mix.

The urgency of the task appeared to crowd out an address the president might have delivered instead, one that lingered on the accomplishments of his two terms in office. Indeed, listing his achievements, he echoed his much-mocked 2008 declaration that his victory in the Democratic primary marked “the moment when the rise of the oceans began to slow.” But Obama collapsed that back-patting into a relatively short space in the beginning of his remarks.

The rest, Obama devoted to building up Clinton as a tireless and potent advocate for change — “she never ever quits,” he said — while ravaging Trump as a divisive manipulator with authoritarian instincts. “Anyone who threatens our values, whether fascists or communists or jihadists or homegrown demagogues, will always fail in the end,” he said.

The speech amounted to an opening salvo from a president who plans to be an active force on the campaign trail. That stands to defy recent tradition, by which ebbing popularity forces outgoing two-term presidents to the sidelines. But Obama’s support now hovers reliably above the 50 percent mark, and Clinton has made clear she wants to use him as much as possible heading into the fall.

On Wednesday, Obama sought to rally constituencies across the ideological spectrum. He reminded conservatives of their commitment to checking the strongman brand of government Trump is offering. “Our power doesn’t come from some self-declared savior promising that he alone can restore order as long as we do things his way. We don’t look to be ruled,” Obama said. And the message out of the GOP’s convention in Cleveland “wasn’t particularly Republican and it sure wasn’t conservative,” he said. “There were no serious solutions to pressing problems. Just the fanning of resentments and blame and hate and anger.”

To those on the left still not ready to rally from Bernie Sanders to Clinton, Obama admonished, “If you’re serious about our democracy, you can’t afford to stay home just because she might not align with you on every issue.”

Clinton’s historically high unfavorable ratings are second only to Trump’s, and Obama acknowledged she’s “got her share of critics,” a fact he chalked up to a long public life. “She knows that sometimes during those 40 years she’s made mistakes, just like I have, just like we all do. That’s what happens when we try,” he said. But, Obama suggested, those scars just mean she’s ready to serve. “Hillary Clinton is that woman in the arena. She’s been there for us, even if we haven’t always noticed.”