Trump signed an executive order designating Antifa as a "domestic terrorist organization.”

The order directs federal agencies to "utilize all applicable authorities to investigate, disrupt, and dismantle any and all illegal operations — especially those involving terrorist actions — conducted by Antifa or any person claiming to act on behalf of Antifa."

The order also directs any necessary investigations and prosecutions of "those who fund such operations."

The order that Trump signed describes the organization as one that "recruits, trains, and radicalizes young Americans to engage in this violence and suppression of political activity, then employs elaborate means and mechanisms to shield the identities of its operatives, conceal its funding sources and operations in an effort to frustrate law enforcement, and recruit additional members."

The order also claims that antifa members coordinate with other organizations "for the purpose of spreading, fomenting, and advancing political violence and suppressing lawful political speech."

"This organized effort designed to achieve policy objectives by coercion and intimidation is domestic terrorism," the order said.

It is not immediately clear how the domestic terrorist organization designation would be made for antifa, which is an umbrella description for far-left-leaning militant groups opposing fascists and neo-Nazis. Antifa does not have a publicly known centralized structure or leadership.

-ABC News’ Michelle Stoddart

Lindsey Halligan was officially sworn in as the interim U.S. Attorney for the Eastern District of Virginia, Attorney General Pam Bondi announced on social media Monday.

Halligan, who most recently worked in the White House staff secretary's office, represented President Trump for a time during the classified documents investigation.

Trump said Saturday that he would appoint his former attorney to lead the key federal prosecutor's office after the previous head, Erik Siebert, resigned his position amid pressure from Trump administration officials to bring a criminal case against New York Attorney General Letitia James.

President Trump made an announcement from the Oval Office on autism, flanked by Health and Human Services Secretary Robert F. Kennedy Jr. and Centers for Medicare & Medicaid Services Administrator Mehmet Oz.

"Today, we're delighted to be joined by America's top medical and public health professionals as we announced historic steps to confront the crisis of autism. Horrible, horrible crisis," Trump said.

He and his top officials stated the use of Tylenol during pregnancy may be linked to an increased risk of autism.

Trump said the Food and Drug Administration will begin notifying physicians immediately that it is "strongly recommending that women limit Tylenol use during pregnancy unless medically necessary."

"They are strongly recommending that women limit Tylenol use during pregnancy unless medically necessary," Trump said. "That's, for instance, in cases of extremely high fever."

Studies on this question have not shown a direct cause and effect. Some studies point to a possible link, but major medical groups have evaluated the evidence and continue to recommend acetaminophen as the safest painkiller during pregnancy.

-Mary Kekatos, Cheyenne Haslett and Sony Salzman

White House press secretary Karoline Leavitt said that President Donald Trump will sign an executive order designating Antifa as a terror organization as early as Monday afternoon.

"Well, Antifa is going to be designated a domestic terrorist organization. The president intends to sign that executive order very soon, as soon as it's drafted, as soon as today -- later this afternoon," Leavitt told reporters during Monday's briefing. Though currently, federal law does not allow for U.S. organizations to be labeled "terrorist" groups.

Leavitt also reiterated Trump's pledge to go after left-leaning organizations he claims contribute to political violence.

"Enough is enough. As President Trump has promised, he will directly address the dark sources funding and supporting this domestic terrorism to finally restore order in our country. The American people can expect further very strong action on this very soon," Leavitt told reporters at Monday's briefing, after listing several examples of political violence against Republican figures while not mentioning recent attacks against Democrats.