Hillary Clinton has cast herself as a unifier for divided times, an experienced leader steeled for a volatile world - and aggressively challenged Donald Trump's ability to do the same.
"Imagine him in the Oval Office facing a real crisis," the former US secretary of state and first lady said, as she accepted the Democratic nomination for president early on Friday.
"A man you can bait with a tweet is not a man we can trust with nuclear weapons."
Clinton took the stage to roaring applause from flag-waving delegates on the final night of the Democratic convention in Philadelphia, relishing her nomination as the first woman to lead a major US political party.
But her real audience was the millions of voters watching at home, many of whom may welcome her experience, but question her character.
She acknowledged those concerns briefly, saying: "I get it that some people just don't know what to make of me."
But her primary focus was persuading Americans to not be seduced by Trump's vague promises to restore economic security and fend off threats from abroad.
Clinton said the US needed a leader who would work with allies to keep America safe.
The presidential election presented a stark choice on national security, she said, with the US facing "determined enemies that must be defeated".
She said people wanted "steady leadership", vowing to stand by Nato allies against any Russian threats.
And she pledged to defeat the Islamic State group with air strikes and support for local ground forces, while authorising a "surge" in intelligence to prevent terrorist attacks.
"We will prevail," she said.
Clinton now has just over three months to persuade Americans that Republican presidential candidate Trump is unfit for the Oval Office and overcome the visceral connection he has with some voters in a way the Democratic nominee does not.