On Wednesday, cap and trade finally came to the Senate. Sens. John Kerry (D-Mass.) and Barbara Boxer (D-Calif.) unveiled their their climate change legislation in response to the bill that narrowly passed the House earlier this year.

Kerry was optimistic that his bill would pass. “I’m convinced it has a shot,” he said in an interview with MSNBC. But the response to both the Kerry-Boxer legislation and the concept of cap and trade more generally has been less than overwhelming.

Sen. Mary Landrieu (D-La.) told Roll Call, “I am not committed to [carbon] cap-and-trade under any circumstance.” Sen. Evan Bayh (D-Ind.) punted, saying, “It’s a difficult issue.” Sen. Blanche Lincoln (D-Ark.) came out in favor of dropping cap and trade from any climate change bill back in August, preferring to focus on renewable energy instead. “The problem of doing both of them together is that it becomes too big of a lift,” she said at the time. “I see the cap-and-trade being a real problem.”

Kerry-Boxer is actually tougher in one key respect than the Waxman-Markey bill that passed the House. The Senate version requires a 20 percent reduction in carbon emissions by 2020. The House’s requirement is 17 percent. This has already cost the support of Sen. Jay Rockefeller (D-W. Va.), who wants any bill to address the needs of his coal-mining state.

“The climate legislation proposed today by Senators Boxer and Kerry is a disappointing step in the wrong direction and I am against it,” Rockefeller said in a statement. “Requiring 20 percent emission reductions by 2020 is unrealistic and harmful — it is simply not enough time to deploy the carbon capture and storage (CCS) and energy efficiency technologies we need.  Period.”

Republican defections may be few and far between. John McCain campaigned in 2008 as a supporter of cap and trade, co-sponsoring a bill taking that approach to carbon emissions with Sen. Joe Lieberman (I-CT). But when Reuters asked him if he supported the Kerry-Boxer bill, he replied, “Of course not. Never, never, never.” McCain is reportedly steamed about the short shrift the legislation gives to nuclear power.

If you think it is difficult to cobble together a health care bill that will win majority support, cap and trade is even more difficult. As Rockefeller’s Senate office notes, at least six different committees have jurisdiction over such legislation. There is a tug of war going on over the bill’s precise wording from both the left and right wings of the Democratic Party. Among Democrats alone, moderates and those who hail from energy-producing or manufacturing states that will be particularly hard hit are balking. So are some liberals like Sen. Russ Feingold (D-Wis.) who fear the regressiveness of a national energy tax and its impact on American competitiveness when other countries don’t follow suit.

All told, sources tell TAS that as many as 15 Senate Democrats are either opposed to cap and trade or on the fence. It would take as few as four to deny the majority the votes for cloture, which means that Kerry-Boxer would fall to a filibuster unless the Democratic leadership — already tangled in the weeds of health care — wanted to try to ram it through using the reconciliation process.

Obama budget director Peter Orszag previously estimated that a 15 percent reduction in emissions would cause the average American family to pay $1,300 in additional utility costs per year. That’s a smaller reduction than either the House or Senate version anticipates. The National Association of Manufacturers is predicting a loss of 3 to 4 million jobs under cap and trade, as businesses escape its costs by accelerating the shipping of jobs overseas. These concerns — and the effectiveness of Republican criticisms of “cap and tax” and the “light bulb tax” — are also giving swing-state Democrats pause.

“The more information Americans find out about the ‘cap and trade’ energy tax,” Congressman Steve Scalise (R-La.) told TAS in May, “the more they don’t like this attempt to impose a national tax on energy while shipping millions of American jobs overseas.” That is true of the Democrats representing them, too.

Debate over Kerry-Boxer is just beginning, and there remain influential Democratic constituencies that ardently favor cap and trade. If the health care bill stagnates due to an intraparty fight over the public option, pressure will mount on Senate Democrats to make progress on climate change legislation. But if the early signals are any indication, it looks like John Kerry has his work cut out for him.