What are they going to do? Cut off the federal teet if they interfere with their plans.When the feds fail to act, Article I, Section 10, Clause 3, would appear to allow the several states, or any one of them, liberty to defend their borders, sovereignty, and general welfare. I would define their current situation as imminent danger.
Let the Feds sue. What can the Feds do, fine the state? Send in troops to take over the state? Do you think the Supreme Court would even try such a case? In the mean time, do what is necessary to protect your people, your sovereignty, your health, your prosperity, and your property. It is an invasion.
As a side note, Congress has the power to call forth the militia to repel invasions (Article I, Section 8, Clause 15.). I do believe Congress has dropped the ball on this debacle on our borders.
Woody