Michelle Obama offered a pointed critique of Donald Trump’s temperament on Wednesday, arguing that “a president can’t just pop off” when he or she is upset.

Speaking at a rally in Philadelphia for Democratic nominee Hillary Clinton, the first lady challenged Trump’s claim from Monday’s debate that he has a “much better temperament” than Clinton. While Obama didn’t mention Trump by name, the target of her condemnation was clear.

“When it comes to the qualifications we should demand in a president, to start with, we need someone who will take the job seriously. Someone who will study and prepare so that they understand the issues better than anyone on their team,” Obama said. “We need someone who is steady and measured, because when making life-or-death, war-or-peace decisions, a president can’t just pop off or lash out irrationally. No, we need an adult in the White House.”

Watch the clip of Obama’s remarks above.

The first lady called back to a number of things Trump has said this week, including his comments about former Miss Universe Alicia Machado’s weight and appearance, and his boast that not paying taxes makes him “smart.”

“The presidency doesn’t change who you are. It reveals who you are,” she said.

“If a candidate is erratic and threatening, if a candidate traffics in prejudice, fears and lies on the campaign trail, if a candidate thinks that not paying taxes makes you smart, or that it’s good business when people lose their homes, if a candidate regularly and flippantly makes cruel and insulting comments about women, about how we look, how we act ― well, sadly, that’s who that candidate really is,” she went on. “That is the kind of president they’ll be.”

Obama also took on the GOP nominee for refusing to apologize for perpetuating conspiracy theories about President Barack Obama’s birthplace. She argued that a brief press conference does not erase the years Trump spent pushing racist birther claims.

“[Birther questions were] deliberately designed to undermine his presidency [and] cannot be blamed on others or swept under the rug by an insincere sentence uttered at a press conference,” Obama said. “I think Barack has answered these questions with the example he’s set and the dignity he’s shown by going high when they go low.”

The first lady made similar remarks at a Clinton rally earlier this month.

Editor’s note: Donald Trump regularly incites political violence and is a serial liar, rampant xenophobe, racist, misogynist and birther who has repeatedly pledged to ban all Muslims — 1.6 billion members of an entire religion — from entering the U.S.