When he took office, Trump signed an executive order declaring a national emergency at the U.S.–Mexico border. He also directed Defense Secretary Pete Hegseth and Homeland Security Secretary Kristi Noem to provide a report within 90 days about the state of the border to determine “whether to invoke the Insurrection Act of 1807.”
That means April 20th.
When it's invoked, the Insurrection Act gives the president the authority to deploy the U.S. military or National Guard inside the country to suppress events such as rebellion, insurrection and civil disorder. It provides an exception to the Posse Comitatus Act of 1878, which limits the use of military personnel under federal command for law enforcement within the US.
If you think this is unlikely, don't forget that the Trump gang fired the nation’s top uniformed officer and also the top uniformed lawyers at the Army, Navy and Air Force, all of whom would probably put breaks on reckless actions like this.
So, it's time to learn about the Insurrection Act:
https://en.wikipedia.org/wiki/Insurrection_Act_of_1807
It can be activated in 3 ways, and the 2 most likely now are:
• to address an insurrection, in any state, which makes it impracticable to enforce the law
or
• to address an insurrection, domestic violence, unlawful combination or conspiracy, in any state, which results in the deprivation of constitutionally secured rights, and where the state is unable, fails, or refuses to protect said rights
The article here talks about some people wargaming scenarios for what happens if Trump invokes the Insurrection act, and also some things we can do if he does:
https://truthout.org/articles/what-should-we-do-if-trump-invokes-the-insurrection-act/