In theory, the National Guard could be put under Federal command by Trump. He wouldn't be able to use them for law enforcement, but he could keep them sequestered and unable to act in the case of a conflict. It'd be similar to what Eisenhower did in Arkansas. There, the governor mobilised the National Guard to prevent desegregation of schools, so Eisenhower effectively took command of them and prevented them from being used.
Trump's advisers likely know this, because they were looking at using the National Guard to aid in deportations back in 2017.