Mike Waltz, who played a central role in the Signal-gate, is now out as Trump's National Security Advisor, but why did he decide to resign?

National security adviser Mike Waltz is leaving his White House post, although soon after reports about his departure were published, President Trump announced he plans to nominate him to be ambassador to the United Nations.

National security adviser Mike Waltz is expected to depart from the Trump administration in the coming days, two sources familiar with the matter told CNN, the first major staff shakeup since the president took office in January.