Mike Waltz out as national security adviser

• Waltz was Trump's fifth national security adviser in just over four years as president, and he lasted less than four months in the role.

Why it matters: "Signalgate" was a big strike against Waltz, but the National Security Council was also embroiled in a power struggle and targeted for internal criticism by Trump allies. Waltz's deputy Alex Wong is expected to depart, and several other senior NSC officials were fired last month.

How it happened: While administration officials argued no classified details were discussed in the Signal messages published by The Atlantic, security experts and lawmakers said Waltz's mix-up sparked massive concerns about the way administration officials share and store secure information.

• Officials in the chat discussed the timing, sequencing and results of March 15 strikes against the Houthi rebels.
• President Trump had previously made clear he did not intend to fire Waltz over the scandal.

Friction point: Signalgate prompted several Democratic lawmakers to call for Waltz and Defense Secretary Pete Hegseth, who shared a timeline of the proposed strikes in the chat, to be fired or resign over the leak.

• Hegseth has faced an extremely tumultuous month since, with several of his closest advisers pushed out and some of them warning the Pentagon had devolved into chaos. Trump has denied any plans to fire Hegseth.
• Mark Halperin was first to report that Waltz was expected to be pushed out.

The intrigue: White House envoy Steve Witkoff has already been floated to replace Waltz on a permanent basis but he is not interested in the job, a source familiar told Axios.

This is a breaking news story and has been updated throughout.

Go deeper: Hegseth's leaked texts: "THIS IS WHEN THE FIRST BOMBS WILL DEFINITELY DROP"