So far, it’s been a pretty calm protest. There isn’t a strong basis to call in the NG for crowd control. It would just make Walker look bad if he did that at this point. If the thugs escalate matters to the damage or violence level, then Walker will have no choice.
My take on Walker is that he’s quite a shrewd guy who plays his cards very close to the vest. He seems to have a lot of self control and does not allow himself to be provoked. He’s a cool customer.
If the Capitol has been invaded and occupied while legislators and staff are trapped in ther office then I’d say they have grounds.