Trump says 3rd term isn't a joke, despite term limit

Democratic Sen. Mark Warner, the vice chairman of the Senate Select Committee on Intelligence, took a moment in his opening statement during Tuesday's hearing on worldwide threats to criticize the Trump administration's use of a Signal chat to discuss sensitive military information -- which a journalist was inadvertently added to.

"If this was the case of a military officer or an intelligence officer and they had this kind of behavior, they would be fired," Warner said.

"This is one more example of the kind of sloppy, careless, incompetent behavior, particularly towards classified information -- that this is not a one-off or a first time error," Warner said of the Trump administration.

President Donald Trump told NBC News he remains confident in his national security advisor, Michael Waltz, after the use of an unsecured message chain to discuss a U.S. attack on Houthis in Yemen.

"Michael Waltz has learned a lesson, and he's a good man," Trump told NBC correspondent Garrett Haake.

The Atlantic editor Jeffrey Goldberg, who was inadvertently added to the Signal group chat, told ABC News Live anchor Linsey Davis that he initially responded to a request to connect by someone purporting to be Waltz and the user identified as Waltz put together a group chat with other high-ranking White House officials to discuss military action in Yemen.

Amid scrutiny over the Trump administration's use of an unsecured message chain to discuss sensitive war plans, some top officials are slated to appear before lawmakers for a previously scheduled hearing on worldwide threats.

Director of National Intelligence Tulsi Gabbard, CIA Director John Ratcliffe, FBI Director Kash Patel and National Security Agency Director Timothy Haugh will testify at 10 a.m. ET before the Senate Select Committee on Intelligence.

Republican Sen. Tom Cotton, the chairman of the panel, said on Fox News on Tuesday morning that the Signal chain will "obviously" be discussed during the hearing.

Defense Secretary Pete Hegseth denied that war plans were sent over a Signal group chat in his first comments about The Atlantic story that broke while he was en route to Hawaii.

"I've heard how it was characterized. Nobody was texting war plans, and that's all I have to say about that," Hegseth told reporters in brief remarks after arriving in Honolulu for a layover on a trip to Asia.

He also criticized Atlantic editor-in-chief Jeffrey Goldberg, the article’s author, as "a deceitful and highly discredited, so-called journalist who's made a profession of peddling hoaxes time and time again."

"This is the guy that pedals in garbage. This is what he does," he added.

Top Democrats have called for an investigation into the incident.

"The leak of sensitive national security information by the Trump administration on a non-classified system is completely outrageous and shocks the conscience," House Minority Leader Hakeem Jeffries said in a statement.

-ABC News' Luis Martinez