An upstate New York man recently was charged with making death threats against her.
White House press secretary Sarah Sanders defended Trump earlier yesterday, saying the President has a duty to highlight Omar's history of making comments that others deem anti-Semitic or otherwise offensive and that he wished no "ill will" upon the first-term lawmaker.
But Omar said that since Trump retweeted the video on Saturday, she's received many threats on her life that referred or replied to the posted video.
"Violent crimes and other acts of hate by right-wing extremists and white nationalists are on the rise in this country and around the world," she said.
"We can no longer ignore that they are being encouraged by the occupant of the highest office in the land." She said: "We are all Americans."
Earlier, Pelosi issued a statement while travelling in London saying she had spoken with congressional authorities "to ensure that Capitol Police are conducting a security assessment to safeguard Congresswoman Omar, her family and her staff".
Pelosi said officials would continue to monitor and assess threats against Omar, and called on Trump to discourage such behaviour.
"The President's words weigh a tonne, and his hateful and inflammatory rhetoric creates real danger," Pelosi said. "President Trump must take down his disrespectful and dangerous video."
The video in Trump's tweet included a snippet from a recent speech Omar gave to the Council on American-Islamic Relations (Cair), in which she described the September 11, 2001, terrorist attack on the World Trade Centre as "some people did something", along with news footage of the hijacked airplanes hitting the Twin Towers. Trump captioned his tweet with: "WE WILL NEVER FORGET!"
On Friday the New York Post ran a photo of the burning, smoking Twin Towers on its cover with the headline "Rep. Ilhan Omar: 9/11 Was 'Some People Did Something'." Beneath that, in large bold letters, it said: "Here's your something."
Critics accuse Omar of being flippant in describing the perpetrators of the attacks that killed nearly 3000 people.
She later sought to defend herself by tweeting a quote from President George W. Bush, in which the Republican president referred to the attackers as "people" just days after 9/11.
Omar's quote came from a 20-minute speech she gave to Cair in Los Angeles on 23 March in which she discussed issues affecting the community like Islamophobia and the recent mosque attack in Christchurch.
Rather than trying to trivialise the 9/11 attacks, she was pointing out that as a result of them Muslims in general saw their civil liberties eroded, and she advocated for activism.
She said: "Here's the truth. For far too long we have lived with the discomfort of being a second-class citizen and, frankly, I'm tired of it, and every single Muslim in this country should be tired of it. Cair was founded after 9/11 because they recognised that some people did something and that all of us were starting to lose access to our civil liberties."
After the Washington Post fact-checked the statement to clarify Cair was actually founded in 1994, a spokesman for Omar told the paper that she misspoke and meant to say the organisation's size had doubled after the attacks.
Neither Trump's tweet nor the video included Omar's full quote or the context of her comments. The tweet was posted atop Trump's Twitter feed for much of yesterday, with more than 9 million views. It remained lower in the feed after Pelosi requested that the video be pulled.
Omar is among a group of first-term members of Congress who have challenged the party from the inside. She has repeatedly pushed fellow Democrats into uncomfortable territory with comments about Israel and the strength of the Jewish state's influence in Washington.
But many rushed to her support after Trump's attack.
Senator Elizabeth Warren, who is seeking to become the Democratic party's presidential candidate, wrote 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."
Independent Senator Bernie Sanders who is also a Democratic presidential candidate, wrote on Twitter: "Ilhan Omar is a leader with strength and courage. She won't back down to Trump's racism and hate, and neither will we. The disgusting and dangerous attacks against her must end."
Under the Twitter hashtag #IStandWithIlhanOmar, Star Trek actor George Takei, wrote, referring to the Japanese attack in 1941 that drew the US into World War II: "When I was a child, it was Japanese Americans who were vilified as the enemy after Pearl Harbor. No one stood up for us, and 120,000 of us were sent to internment camps. I swore that I'd dedicate my life to ensure this never happens again in America."
What she said
• Ilhan Omar has been widely criticised for saying "some people did something" when referring to the 9/11 attacks. She was speaking to the Council on American-Islamic Relations (Cair).
• The full quote is: "Here's the truth. For far too long we have lived with the discomfort of being a second-class citizen and, frankly, I'm tired of it, and every single Muslim in this country should be tired of it. Cair was founded after 9/11 because they recognised that some people did something and that all of us were starting to lose access to our civil liberties."
- AP, Washington Post