On behalf of Senate Majority Leader Bill Frist, Republican Sen. John Cornyn just filed a cloture motion on the confirmation of Priscilla Owen -- the procedural step required to set up a vote on whether debate must end and a floor vote be taken.
Under the Senate's rules, the cloture motion will ripen on Tuesday, at which time senators will vote whether or not to cut off debate on Owen's nomination. Presuming that Democrats remain united, they'll have the votes to defeat that motion, which requires 60 votes to pass. Once that happens, Frist will be in the position to trigger the nuclear option.
Tim Grieve is a senior writer and the author of Salon's War Room blog.