Hillary Clinton on Thursday delivered the sharpest attack yet against presumptive Republican presidential nominee Donald Trump, calling him “temperamentally unfit” to be commander-in-chief and arguing his election would be a “historic mistake.”

“I believe the person the Republicans have nominated for president cannot do the job,” Clinton said during the speech in San Diego, California.

Aides billed the speech as a foreign policy address, but Clinton hit Trump on issues at home and abroad – saying in no uncertain terms that a Trump presidency would be disastrous.

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“Donald Trump’s ideas aren’t just different - they are dangerously incoherent. They’re not even really ideas - just a series of bizarre rants, personal feuds, and outright lies,” she said. “He’s not just unprepared - he’s temperamentally unfit to hold an office that requires knowledge, stability and immense responsibility.”

It was the first major policy speech delivered by Clinton since Trump clinched the Republican nomination last month. It was largely a mashup of past policy addresses on issues like dealing with ISIS, the Iran Deal and the growing threat of terrorist attacks around the globe. But in it, Clinton sharply undercut a number of Trump’s past statements while questioning his mental stability.

Clinton called her GOP rival “thin skinned,” “angry,” and questioned whether he realized “he’s talking about nuclear war” when he said Japan should have nuclear weapons.

“Even if I weren’t in this race, I’d be doing everything I could to make sure Donald Trump never becomes president because I believe he’ll take our country down a truly dangerous path,” Clinton said.

Clinton has slammed Trump twice as being “unqualified and unfit” for the presidency over the past 24 hours. On Wednesday, she called him a “fraud” outright for his connection to Trump University.

During Thursday’s speech, Trump tweeted Clinton “no longer has credibility” after “too much failure in office.” And almost on cue, Clinton predicted Trump would be sending “nasty tweets” while she was speaking.

Bad performance by Crooked Hillary Clinton! Reading poorly from the telepromter! She doesn’t even look presidential! — Donald J. Trump (@realDonaldTrump) June 2, 2016

Imagine if he had not just his Twitter account at his disposal when he’s angry, but America’s entire arsenal. https://t.co/e7M2CV3sj6 — Hillary Clinton (@HillaryClinton) June 2, 2016

The former secretary of state has a major advantage over Trump on foreign policy, according to this month’s NBC News/Wall Street Journal poll. Fifty-six percent of registered voters said Clinton would be better at handling foreign policy, while just 29 percent chose Trump.

“I have a lot of faith that the American people will make the right decision…Because making Donald Trump our commander-in-chief would be a historic mistake,” Clinton said.

Though the speech was entirely focused on Trump and she didn’t mention her primary rival Bernie Sanders once, Clinton is still battling the Vermont senator in the Golden State. Thursday’s event in San Diego kicked off a 5-day barnstorm through California ahead of next week’s primary. Her campaign hopes a victory in New Jersey, which also votes next week, will allow her to clinch the Democratic nomination even before the polls close out west.

This article originally appeared on NBCNews.com.