Schumer has faced pressure back home, including occasional protests outside his Brooklyn apartment by activists urging him to take a stronger stand against Trump across a range of issues. Of late, one of those groups, Indivisible Nation Brooklyn, has prioritized climate issues and pushed Schumer to endorse the Green New Deal and oppose USMCA. Schumer’s vote on the measure is “progress,” says Liat Olenick, a co-president of the group. “It’s positive, and we always want to acknowledge positive things.”

Schumer declined to comment beyond his statement. But his office noted that the longtime senator has been placing a higher priority on addressing climate change in recent years. The Democrats’ 2018 campaign platform pledged that any new trade agreement would address climate change, and last year Schumer established a Democratic special committee to address the crisis after Republicans refused to create an official Senate panel.

If primary considerations were a factor in Schumer’s vote, he’s likely not alone. The Democratic defections on USMCA underscore the growing threat incumbent lawmakers feel from progressive primary challengers, who are building on the model popularized by the Tea Party to push the party leftward. Just 38 House Democrats voted against the trade deal, but several of them are already facing aggressive primary challengers. The opponents include two representatives, Eliot Engel of New York and William Lacy Clay of Missouri, whose challengers have been endorsed by Justice Democrats.