[andyk]

what grounds would the ACLU have to bring suit if Hannity did enter the US illegally?

Well, they would obviously have no grounds to bring suit. I haven't heard or read anything that indicates they're attempting to sue (unless I missed it in this thread). Here's what they wanted in this case:

Apparently upset at Hannity’s drawing interest to the good work of the Minutemen, Arizona State Rep. Kyrsten Sinema, under the auspices of the ACLU, demanded Hannity’s arrest.

[Big Digger]

OK then, what is the ACLU's standing to demand the arrest of anyone?