Biden can declare a public health crisis at any time. He can declare a national security emergency just based on the number of known terrorists they're catching on the border.

No, he can't.

I mean, sure, he could say there's a public health crisis. But there isn't, so it would never hold up in court. You can't point to the fact that TB rates are slightly higher in Mexico than in the U.S. as a reason to close the border just to asylum seekers altogether. Several hundred million people cross the Mexican border every year as part of routine traffic, there's no evidence that TB rates are going up in areas where migrants are present, the Administration has the power and ability to both screen migrants for TB (and other illnesses) and detain any migrant they want for any length of time if they have an illness. It's so obviously pretextual it would never hold up in court.

The same is true of any "national security emergency." What's the emergency? Is there any particular reason to think that if terrorists wanted to get into the U.S. for the purpose of committing a terrorist act, the way they would do it is by walking in and surrendering immediately to the Border Patrol? Rather than, say, getting on a plane so they can enter without immediately being detained by the authorities (like all the 9/11 terrorists did)?

At some point, your lawyers have to be able to stand in front of judges and persuade them that your actions that you claim are justified by public health crises or national security emergencies are in fact those things and not a backdoor effort to try to address immigration issues. During Covid, those measures had a legitimate public health basis, as the U.S. was implementing border control policies in a host of circumstances, barring entry (and imposing additional entry requirements) to everyone, asylee or not. Those circumstances are long, long gone.