US President Donald Trump today expressed support for his National Security Adviser, Michael Waltz, after a magazine journalist said yesterday that Waltz had accidentally included him in a discussion of highly sensitive war plans on the messaging app Signal, Reuters reported.

“Michael Waltz has learned a lesson, and he’s a good man,” Trump told NBC News in a phone interview.

US senators were set to grill Trump’s top intelligence officials today about the apparent breach, which triggered outrage and disbelief among Democrats and national security experts.

Jeffrey Goldberg, editor-in-chief of the Atlantic, said in a report that Waltz unexpectedly added him on 13 March to an encrypted chat group on the Signal messaging app coordinating US action against Yemen’s Houthi group.

National Security Council spokesperson Brian Hughes said the chat group appeared to be authentic. The White House said it was looking into how Goldberg’s number was added to the thread.

Democrats – and some of Trump’s fellow Republicans – called for an investigation of what appeared to be a major security breach. Classified and sensitive information is not supposed to be shared on commercial mobile phone apps, and unknown numbers – such as Goldberg’s – should not be included.

Members of the Senate Intelligence Committee were to question two of the administration officials on the chat – Director of National Intelligence Tulsi Gabbard and CIA Director John Ratcliffe – today during the panel’s annual hearing on Worldwide Threats to US Security.

In his opening statement, Senator Mark Warner, the Democratic vice chairman of the intelligence committee, said a military or intelligence officer who took similar action would be fired.

“Yesterday, we stunningly learned that senior members of this administration, and according to reports, two of our witnesses here today, were members of a group chat that discussed highly sensitive and likely classified information that supposedly even included weapons packages, targets and timing and included the name of an active CIA agent,” he said.

White House Press Secretary Karoline Leavitt accused Goldberg of sensationalising the story in a post on X and asserted that no war plans were discussed and no classified material was sent to the thread.

In his article, Goldberg wrote that hours before the US launched strikes against Yemen’s Houthis on 15 March, Defence Secretary Pete Hegseth posted operational details about the plan in the messaging group, “including information about targets, weapons the US would be deploying, and attack sequencing.”

His report omitted the details out of national security concerns, but Goldberg termed it a “shockingly reckless” use of a Signal chat.

Security risk

It remained unclear why the officials chose to chat via Signal rather than the secure government channels typically used for sensitive discussions.

Accounts that appeared to represent Vice President JD Vance, U.S. Secretary of State Marco Rubio, Ratcliffe, Gabbard, Treasury Secretary Scott Bessent, White House chief of staff Susie Wiles, and senior National Security Council officials were assembled in the chat group, Goldberg wrote.

While some Democrats called for officials on the chat to lose their security clearances or resign, there was no immediate word on whether any official would face consequences.

White House officials and some fellow Republicans instead stressed that the attack on the Houthis had gone off without a hitch.