Washington (CNN) President Donald Trump, who accused a Muslim lawmaker this week of diminishing 9/11 , is wielding a hallowed date that he, himself, has been accused of wrapping in mistruths, self-aggrandizement and Islamophobia.

And he has spread a lie that across the Hudson River in New Jersey, "thousands and thousands of people were cheering as that building was coming down," a baseless tale he relayed to campaign audiences at the same time he was promising to ban all Muslims from entering the country.

The terror attack nearly 18 years ago on Trump's hometown has long been woven into his political message, whether it is deriding past leaders for ignoring the threat of Islamic terrorism or using the day to signal to voters an underlying threat of continued attacks.

But he has not always treated the day with great reverence or gravity, which is precisely the suggestion he seemed to make this week against Rep. Ilhan Omar, tweeting a video that featured images of the attack spliced with clips of Omar decrying acts of hatred against Muslims that occurred in its aftermath.

"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," Omar said, speaking to a California chapter of the Council on American-Islamic Relations. "They recognized that some people did something and that all of us were starting to lose access to civil liberties."

Some of Omar's critics have said her remarks -- specifically her description of the event as "some people did something" -- were dismissive. Omar and her Democratic supporters say that is taken without context, and that her point about increased threats against Muslims shouldn't be taken lightly.

Already, Trump's use of the video to attack Omar, the freshman Democrat says, has led to an increase in threats on her life, according to a statement she issued on Sunday. And it has caused House Speaker Nancy Pelosi to consult with the House Sergeant at Arms on a security assessment.

That did not stop Trump from continuing to assail both Omar and Pelosi on Monday.

"Before Nancy, who has lost all control of Congress and is getting nothing done, decides to defend her leader, Rep. Omar, she should look at the anti-Semitic, anti-Israel and ungrateful U.S. HATE statements Omar has made," he wrote on Twitter. "She is out of control, except for her control of Nancy!"

Trump traveled to Omar's home state of Minnesota on Monday to participate in a tax roundtable event, an occurrence the congresswoman said in her statement was cause for concern.

"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," Omar wrote. "We can no longer ignore that they are being encouraged by the occupant of the highest office in the land."

The White House has insisted that is not the case.

"Certainly the President is wishing no ill will and certainly not violence towards anyone," White House press secretary Sarah Sanders said on ABC's "This Week" on Sunday.

'I think Islam hates us'

Still, Trump has made little attempt in the past to disguise his warnings against Islam and Muslims, including using the 9/11 attacks as a cautionary tale.

"I think Islam hates us," Trump told CNN's Anderson Cooper in 2016 , deploring the "tremendous hatred" that he said partly defined the religion. He maintained the war was against radical Islam, but said, "It's very hard to define. It's very hard to separate. Because you don't know who's who."

That assertion came amid a campaign that relied heavily on aspersions and alerts about Islam, including his vow to halt all Muslims from entering the United States "until our country's representatives can figure out what the hell is going on."

Part of that effort included describing terrorist sympathizers in the United States celebrating as the Twin Towers crumbled on 9/11, a story he refused to recant even after fact-checkers repeatedly identified it as false -- just as some of his other recollections of that day and the weeks afterward were called into doubt.

Trump recalled at a rally in 2015 having been at his Trump Tower apartment windows watching as people jumped from a burning World Trade Center — "I witnessed it, I watched that" -- though geographically that appears impossible, given the distance between the two buildings.

Later, Trump claimed to have traveled to Ground Zero to view damage and help in the aftermath -- "I was there, and I watched, and I helped a little bit" -- but no witnesses have emerged to describe the alleged assistance he claimed to provide.

And he described having "lost hundreds of friends" in the attack, though his campaign at the same wasn't able to identify any of them by name.

'He has no moral authority'

JUST WATCHED Nadler: No issues with Omar 9/11 comment Replay More Videos ... MUST WATCH Nadler: No issues with Omar 9/11 comment 01:49

Trump's own questionable history in describing the attack, and his actions in its wake, have led some to question his standing in using 9/11 to smear his rivals.

"He has no moral authority to be talking about 9/11 at all," said Rep. Jerry Nadler, D-New York, on CNN's "State of the Union" Sunday. Nadler's district includes the World Trade Center.

Nadler cited Trump's receipt of $150,000 in state small business funds after the attack as evidence of the President's craven approach to the disaster. Trump has explained the grant as reimbursement for allowing recovery workers to use one of his buildings, Forty Wall Street, to store supplies. But people involved in the disbursement of the funds have said previously they weren't meant for repayment purposes, according to the New York Daily News

And it's not the only evidence of Trump viewing the potential upside of what remains the deadliest terror attack in American history.

"Forty Wall Street actually was the second-tallest building in downtown Manhattan, and it was, actually, before the World Trade Center, was the tallest. And then when they built the World Trade Center it became known as the second-tallest, and now it's the tallest," he proclaimed in an interview the day of the attack in 2001.

More recently, Trump has similarly brushed aside normal conventions of soberness surrounding the yearly 9/11 anniversary.

"I would like to extend my best wishes to all, even the haters and losers, on this special date, September 11th," he tweeted 2013.

As President, he has participated in somber remembrance events at the White House and elsewhere, but has not desisted in his usual Twitter combat for the day nor attempted a more restrained attitude.

Arriving in Pennsylvania last year at a newly built memorial to victims of Flight 93, Trump flashed a celebratory smile and pumped his fists as he greeted supporters on the tarmac.