Bill McMorris of the Washington Free Beacon highlights an interesting calculation from Democratic presidential contender Bernie Sanders.

Socialist senator Bernie Sanders (I., Vt.) chose to support the interests of environmentalists over the nation’s largest labor union at Tuesday’s debate, saying he will vote against the Trump administration’s renegotiation of NAFTA.

The Senate is expected to vote on the White House’s U.S.-Mexico-Canada Agreement on Thursday. Sanders, a longtime critic of NAFTA and free trade agreements in general, has indicated that he will oppose the deal, despite acknowledging that it would help workers. He defended that position at the debate, saying the trade deal did not do enough to win the approval of environmentalist groups.

“Every major environmental organization has said no to this new trade agreement because it does not even have the phrase ‘climate change’ in it,” Sanders said. “I will not vote for a trade agreement that does not incorporate very, very strong principles to significantly lower fossil fuel emissions in the world.”

The agreement has won the endorsement of the nation’s largest labor unions, many of which saw their members support Trump in Rust Belt states in 2016. The AFL-CIO said that the final agreement is a deal “working people can proudly support.” Sanders has received more than $2 million from labor groups, according to the Center for Responsive Politics, and enjoys a 98 percent lifetime approval rating, according to the AFL-CIO’s legislative scorecard. That score may fall after Thursday’s vote.