Spicer realised he'd stuffed up later in the briefing, when he tried to walk back his comments.
"When it comes to Sarin gas, [Hitler] was not using the gas on his own people the same way that Assad is doing," he said.
"I understand your point. Thank you. I appreciate that. He brought them into the Holocaust centres, I understand that. I was saying in the way that Assad used them where he went into town, dropped them into the middle of town. I appreciate the clarification. That was not the intent."
Despite that, the reaction to Spicer's comments has been a mix of shock and fury. The Anne Frank Centre For Mutual Respect immediately called for him to be fired.
"On Passover no less, Sean Spicer has engaged in Holocaust denial, the most offensive form of fake news imaginable, by denying Hitler gassed millions of Jews to death. Spicer's statement is the most evil slur upon a group of people we have ever heard from a White House press secretary, and President Trump must fire him at once," the centre said.
That strident sentiment was echoed by the Trump administration's political opponents.
"While Jewish families across America celebrate Passover, the chief spokesman of the White House is downplaying the horror of the Holocaust," said senior Democrat Nancy Pelosi.
"Sean Spicer must be fired, and the president must immediately disavow his spokesman's statements. Either he is speaking for the president, or the president should have known better than to hire him."
Spicer later issued another statement clarifying his remarks.
"In no way was I trying to lessen the horrendous nature of the Holocaust. I was trying to draw a distinction of the tactic of using airplaines to drop chemical weapons on population centres. Any attack on innocent people is reprehensible and inexcusable," he said.
That still wasn't enough, so he went back on TV to apologise.
"Frankly, I mistakenly used an inappropriate and insensitive comment about the Holocaust and there is no comparison. For taht I apologise. It was a mistake to do that," Spicer told CNN.
As you'd expect, the backlash on social media was brutal.
Spicer is regularly lampooned on late night sketch shows and especially Saturday Night Live, where Melissa McCarthy has been brought in as a special guest to play him. He just gave the comedians even more fodder.
