Too many Republicans these days have lost their economic bearings. Look no further than a GOP Senate bill that would enact a carbon tariff—i.e., a new tax. In the name of punishing China, the legislation would punish American consumers and businesses.

The Foreign Pollution Fee Act, sponsored by Louisiana’s Bill Cassidy and South Carolina’s Lindsey Graham, could well have been written by the Sierra Club and AFL-CIO. Among the carbon tariff’s biggest advocates is Donald Trump’s former trade adviser Robert Lighthizer, who favors tariffs in principle. So it’s worth deconstructing the misleading arguments that Mr. Cassidy and others are making for climate protectionism.