So the venue that holds 20,000 was still letting people in with no line at the start of the event. Admittedly he did pack the venue full. But this is 1/3rd to 1/5th of his claimed rate of 76,000 to 100,000
I think this is 50/50. Obviously this tweet was to prep for the rally last night. He need to make sure the fear on immigrants was worked up and he could state that millions would be rounded up.
Without the wall being a real issue right now (the funding fight is on hold) he has to use a round up as a way to fire up his base (once again we have seen this historically). Also since the wall is not really a focus right now he can focus some ICE resources to a internal round up giving out some anecdotal numbers cases of catch "bad hombres"