This could be tied in to whatever it is the MX congress has to vote on.
I'm thinking along the lines of money transfers. I'm assuming (I know) that most money transfers would occur at the beginning /end of the month or in the middle. Announcing a sweep for the 23rd and monitoring wire transfers for panic transactions would give you a good idea of from where and which illegals are sending $ out of the US; that is, it isolates them the normal end of month transaction spike.
So, MX vote may have something to do with how to handle $ coming in to MX. Seems to me MX is picking up $ on the cheap as it is now (along with drug revenues). perhaps money transfers are being dealt with to reduce the flow of $ out of the US. That, along with getting contracted sponsors to fork up to pay for any money illegals got from the welfare/social net, will cause a major upheaval in the game as it's being played now.
I think, too, that the sponsors of green card holders are on the hook for back payment of unauthorized payments, not just illegals. That would add a twist to the DACA discussion. Lot involved here.