Sec Espers is correct on announcing the military units providing crowd and riot control will not be carrying firearms. The units will likely be following training and method covered in the US Army Field Manual FM 3-19.15, Civil Disturbance Operations and Civil Disturbances ATP 3-39.33.
For crowd control, they are trained in control methods and non-lethal equipment. Part of civil disobedience crowd control includes an extraction teams, lethal overwatch teams, as well as reserve forces should violence escalate. Other law enforcement such as Capital police, FPS, USSS, and military police are available if firearm response is necessitated.
For the National Guard members, this minimizes the risk of using arms against fellow citizens. It reduces risk of violent protesters getting access to firearms. Utilizes existing training methods and procedures. Probably most important, it eliminates a talking point of media and politicians that the President using armed troops against citizens.
US Army Field Manual FM 3-19.15, Civil Disturbance Operations
https://fas.org/irp/doddir/army/fm3-19-15.pdf
Civil Disturbances ATP 3-39.33
https://armypubs.army.mil/epubs/DR_pubs/DR_a/pdf/web/atp3_39x33.pdf