Emissions Tax: What 2012 Presidential Hopefuls Are Saying

March 30, 2011 -- President Obama called on Congress and the United States to end gridlock and create a new clean energy standard when he unveiled a new energy blueprint today.

But there was a glaring omission from his speech. What he did not mention was a cap-and-trade proposal, which would place limits on how much greenhouse gas a company could emit and allow more energy-efficient companies to sell their unused "emission permits" to companies that might find it harder to reduce their emissions. Republicans defeated such proposals last year by calling them an energy tax. Democrats came within several votes of passing a cap-and-trade proposal last year.

Now Senate Republicans have launched an effort to strip the Environmental Protection Agency of authority to cap carbon emissions.

Most Republicans now oppose imposing mandatory emissions caps on U.S. companies, arguing that it would dent job growth and hurt the U.S. economy. But it wasn't always so. Republicans such as Sens. John McCain and Lindsay Graham once co-sponsored cap-and-trade legislation with Democrats, many of whom say cap-and-trade policies are needed to curb the emissions of dangerous carbon dioxide greenhouse gases.

At least three Republicans currently considering a run for the presidency at one time endorsed a cap-and- trade policy: former Minnesota Gov. Tim Pawlenty, former House Speaker Newt Gingrich and former Massachusetts Gov. Mitt Romney.

Pawlenty went so far this week as to tell conservative radio host Laura Ingraham that his past support for a cap-and-trade policy was a mistake. He apologized for it.

Here's a look at where potential 2012 candidates stand on the controversial issue and how their views have evolved: