TLDR Summary:Theoretically, the most obvious next step required by law for the POTUS to invoke the insurrection act in one or more cities would be to issue a formal proclamation for the rioters to disperse. If the rioters don't disperse per the deadline provided in the proclamation - Insurrection Act kicks in. If you read the following, you can see it's more complicated than that, but that's my simplified opinion after querying GROK about legal requirements for the invocation of the Insurrection Act in L.A., Chicago, and Portland.For the minimally interested, you may want to skip down to the TABLE...