At last, some certain information! Chambliss and Isakson against cloture. Thanks to a reader, this update from CQ:

Georgia Republicans Johnny Isakson and Saxby Chambliss will vote against moving the Senate’s immigration overhaul measure forward, the senators said today.

“I think everybody did a noble effort to try to deal with the problem in a comprehensive way,” Isakson said. “But it became apparent that the confidence level was not there.”

Isakson said he and Chambliss had heard from voters back home that they didn’t have faith in another measure that promises border action because past promises have yet to be fulfilled.

So it seems that, even if Trent Lott won't be moved by voters back home, constituent voices do affect some...

Chambliss and Isakson move to Very Unlikely to Switch.