Trump wrote an executive order setting up the justification to enact the Insurrection Act if the border isn’t ‘under control’ by April 20th.

Within 90 days of the date of this proclamation, the Secretary of Defense and the Secretary of Homeland Security shall submit a joint report to the President about the conditions at the southern border of the United States and any recommendations regarding additional actions that may be necessary to obtain complete operational control of the southern border, including whether to invoke the Insurrection Act of 1807.

https://www.whitehouse.gov/presidential-actions/2025/01/declaring-a-national-emergency-at-the-southern-border-of-the-united-states/