Carbon tax in debate

As I write this, Bill Richardson and Barack Obama are on a New Hampshire stage agreeing that we don't need a carbon tax (and arguing for cap-and-trade instead). Hillary Clinton has just added some vagueness about energy efficiency. Yet cap-and-trade has had a distinctly mixed record where it's been tried, and--unlike a carbon tax--offers only weak incentives to reduce emissions lower than the cap. There's an opportunity here for Republicans to point out that these Democrats are being soft on global warming and on energy independence.