The League of Conservation Voters endorsed Hillary Clinton for President yesterday, and Bernie Sanders supporters are not happy.

Backers of Sanders posted a slew of comments on Facebook and Twitter, suggesting that the League of Conservation Voters’ federal political action committee had made a politically expedient choice. They noted that Clinton did not come out against the contentious Keystone XL pipeline, which Obama vetoed Friday, until September, while her rivals were early opponents.

Several vowed to withhold future donations to LCV in retaliation for the move and either give the money to other environmental groups, or Sanders himself.

“Bernie is obviously the better choice when it comes to environmental issues!!!!” posted Kimberlee Nelson. “He doesn’t have to think twice when it comes to protecting the environment unlike Hillary. ugh.”

LCV’s political folks fired right back.

In an interview Monday evening, LCV Action Fund President Gene Karpinski said ” it’s not surprising that Senator Sanders’ supporters feel passionately” about their candidate.

“We continue to believe Hillary Clinton is best positioned to be an effective leader, and will be the best president on these issues from Day One,” he added.

In determining its endorsement, according to a statement, the political committee of the League of Conservation Voters’ board of directors reviewed questionnaires and conducted in-person interviews with each “pro-environment candidate” in the presidential race. The committee gave its recommendation to the full board of directors, which approved it.

The endorsement process is not the search for truth that the Sanders folks would like it to be. It mixes political expediency, personality, and the desire to back a winner. I’d expect more endorsements like this one to come as the process unfolds.