Gov. Mitt Romney accused EPA administrator Lisa P. Jackson of blocking new coal plant construction in the United States, saying, “The head of the EPA said you can’t build a coal plant. It’s virtually impossible given the regulations.”

There’s no question that new EPA regulations, including limits on mercury and other toxic emissions, and a proposal to curb greenhouse gas emissions on new power plants have made it harder to build new coal-fired power plants.

But the lower price of natural gas, which costs less than a quarter of what it did four years ago, has undercut new coal plants just as much, if not more, than new federal regulations.