Democratic presidential candidates blasted President Trump over the weekend for inciting violence, perpetuating Islamophobia and politicizing the worst day in American history after he escalated attacks on Rep. Ilhan Omar by tweeting a video of her image spliced with footage of the burning Twin Towers on 9/11.

The swift condemnation began Friday night after Trump tweeted the videowith the caption “Never Forget,” and it continued to be a focal point across the campaign trail on Saturday.

Omar, who made history as one of the first two Muslim women elected to Congress, has been attacked by the right this week for saying “some people did something” as part of a larger point she was making about the treatment of Muslim Americans after the 9/11 attacks.

Trump’s tweet was instant fodder for Democrats lining up to run against Trump in the 2020 election.

Shortly after Trump’s tweet, Sen. Elizabeth Warren (D-Mass.) responded forcefully on Twitter: “The President is inciting violence against a sitting Congresswoman — and an entire group of Americans based on their religion. It’s disgusting. It’s shameful. And any elected leader who refuses to condemn it shares responsibility for it.”

South Bend Mayor Pete Buttigieg, who served in Afghanistan, reacted late Friday night over several tweets to Trump‘s attack on Omar.

“Now, a president uses that dark day to incite his base against a member of Congress, as if for sport. As if we learned nothing that day about the workings of hate,” wrote Buttigieg, referring to 9/11. “The president today made America smaller. It is not enough to condemn him; we must model something better.”

About 20 minutes later, Buttigieg added another tweet after he was criticized on the site for not directly mentioning Omar by name.

“The threats against the life of @IlhanMN make clear what is at stake if we fail to do this, and to beat back hate in all its forms,” he wrote.

Former Texas congressman Beto O’Rourke faced similar criticism when he tweeted Friday night: “We are stronger than this president’s hatred and Islamophobia. Do not let him drive us apart or make us afraid.”

Then, on Saturday morning at a town hall in a seafood restaurant near Charleston, S.C., O’Rourke described the president’s tweet and the video it contained and then denounced it in a monologue that lasted several minutes. As he spoke, many in the crowd gasped or exclaimed at the description, then applauded O’Rourke’s response: that the video is a continuation of rhetoric used by the president and his administration against Mexican immigrants, asylum seekers, Muslims and others.

“This is an incitement to violence against Congresswoman Omar, against our fellow Americans who happen to be Muslim,” O’Rourke said.

At the end of a roundtable with voters in Gary, Ind., Sen. Bernie Sanders (I-Vt.) hinted at the controversy, saying that “the function of a president is bringing our people together,” and that the current president was failing at that. “Even conservative presidents have understood that,” Sanders said.

“George W. Bush — I didn’t have a lot in common with him. His views were very different than mine,” Sanders noted. “But remember what he did after 9/11? He walked into a mosque to say that criminals, terrorists, attacked the United States. Not the Muslim people. That was a conservative Republican. We now have a president who for cheap political gain is trying to divide us up.”