Ensign's Conditions: Geraghty has a report on the the conditions for Ensign to switch to vote against cloture:

Sen. John Ensign, R-Nev., has two big amendments/criteria, according to his office. The first is an amendment to close a loophole for Social Security benefits; as the bill is written now, it allows immigrants to collect Social Security if they've committed identity theft or fraud. Ensign contends the bill as it stands encourages identity theft and fraud. The second is another amendment, part of interior enforcement package, is to create an "exit tracking system." Forty percent of illegal immigrants arrive here legally and overstay their visas. Ensign wants to have an exit tracking system to know who's here, who's left.

Bond (h/t a reader) also has his own condition for switching.