Generally that has meant that they are apprehended and released at the border, to try again.
I doubt anything has changed.
That's actually worth asking - I'll pass that question on to Bill Hess today. I know that in the western part of the Tucson sector (Nogales, Sells, Ajo) that crossers are being locked up for up to 6 months prior to court hearings and adjudications, then deportation. This automatically makes them felons when they come back into the US.
It's a zero-tolerance policy that was instituted last summer. I don't know if it is also happening here in the eastern part of the Tucson sector (Douglas, Willcox, Bisbee, and Sierra Vista).