The smart play, I think, will be for Trump to declare that group unlawful terrorists, and that anyone supporting them in any way is in violation of the law. He can cut off Federal funds to Washington. He can seize the bank accounts of anyone providing them money or food or assistance in any way.
It won’t take long for it to most likely first get ugly, then for most of the kids to quit, since it won’t be fun any more, and will quickly get boring. The barriers will last a while, but even they will most likely be pulled down at some point.
Vastly easier to take the wind out of their sails, than to assault them directly.
And the example will be set: support terroristic criminals–and seizing a section of the city clearly violates many laws, over and above what they are most likely doing to people in that area– and you will pay the price.
As always, it’s important not to panic. I never thought Trump would be elected, but he was. It seemed unlikely he would prevail in all his battles, but he has.