“can’t”
Search on “ governor summons national guard” and see when it has happened.
Also, what will cloud a guard’s decision is the potential dishonorable discharge and loss of benefits, sorta like with LEOs, who have never turned down a red flag raid.
This is why the public needs guns on par with the military.
A governor can call the Guard out for state active duty, but he cannot “nationalize” it.
I did a number of state missions for hurricanes, blizzards, etc