1. Mediocre Emissions Limits + Nuke Subsidies: The McCain-Lieberman Bill, now cleverly rebranded the McCain-Lieberman-Obama Bill, is the leading candidate. It establishes a middling cap-and-trade system and ladles on, purely for the purpose of appeasing the right (a skill at which McCain is becoming quite adept), a bunch of nuke subsidies.
2. Mild Emissions Limits + Not Really: Jeff Bingaman (D-N.M.) is proposing a watered down set of caps -- industries would have to "stabilize their emissions by 2020 at levels registered in 2013" -- along with an "escape valve" that would let companies out of it if they, you know, didn't like it or whatever. This thin gruel is said to represent "the center" in the Senate.
3. Tougher Emissions Limits + Boost CAFE Standards + Subsidize Big Corn + Raise Energy Efficiency Standards: Dianne Feinstein (D-Calif.) and Tom Carper (D-Del.) are introducing bills to cap emissions at electric plants and create a cap-and-trade system. Feinstein promises more bills that will raise auto fuel efficiency and energy efficiency standards and dump some money on biofuels.
4. Emissions Limits Equal to the Task at Hand: Sen. Bernie Sanders (I-Vt.) has introduced legislation that would cut U.S. emissions 80% from 1990 levels by 2050 through a combination of mandatory emissions cuts and subsidies to clean energy. Barbara Boxer (D-Calif.) is co-sponsoring and calls it the "gold standard." (Retired Sen. James Jeffords (I-Vt.) introduced it last session.) Sanders concludes:

   As a country that represents only 6% of the world's population but produces 25% of its greenhouse gas emissions, we have a moral obligation to lead the way toward reducing these emissions. For your sake and the sake of your children and grandchildren, we must meet that obligation.

I don't know if it's a coordinated strategy, but Senate Dems are chucking a whole handful of spaghetti at the wall to see what sticks. The advantage of this approach is that the tougher measures makes the weaker measures look moderate, and the sheer number of bills makes inaction look extreme. The disadvantage is that the weakest is pretty damn weak, and all the usual suspects will hone in on it.

I would prefer the Sanders bill, of course, but Dems need 60 votes to get past a filibuster, so they'll have to lure some Republicans -- not to mention intransigent Dems like West Virginia's Robert Byrd.

Note, as several reporters have, that one climate bill is sponsored by what may well turn out to be both parties' leading candidate for president in 2008. Action is happening in this area. The moment has finally arrived.