Presumptive Democratic presidential nominee Hillary Clinton Hillary Diane Rodham ClintonJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Momentum growing among Republicans for Supreme Court vote before Election Day Warning signs flash for Lindsey Graham in South Carolina MORE won the endorsement of the Sierra Club on Thursday.

Michael Brune, the group's executive director, said in a statement that Clinton “will be the strong environmental champion that we need to lead our country,” handing the former secretary of State her second major environmental endorsement of the week.

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“The Sierra Club, like so many Americans, not only wants to protect President Obama’s legacy — we want to expand it,” Brune said in a statement.

“That is something we can accomplish with a Clinton White House, and it’s why the Sierra Club’s members and supporters will work tirelessly to make sure she’s elected this November.”

The Sierra Club waited until after Clinton effectively locked down the Democratic nomination this week before endorsing her over rival Bernie Sanders Bernie SandersNYT editorial board remembers Ginsburg: She 'will forever have two legacies' Two GOP governors urge Republicans to hold off on Supreme Court nominee Sanders knocks McConnell: He's going against Ginsburg's 'dying wishes' MORE.

Tom Steyer, the billionaire Democratic donor who runs the NextGen Climate group, also endorsed Clinton this week, joining the League of Conservation Voters Action and Natural Resources Defense Council Action Fund in signing off on Clinton’s campaign.

Brune praised Sanders for a “hard-fought campaign” that he said “helped elevate climate change and protecting our environment while reducing inequality as key issues in the Democratic Primary.”

And he took aim at presumptive Republican presidential nominee Donald Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE, saying, “The gap on environmental and climate issues between Secretary Clinton and Donald Trump is the largest in U.S. political history.”

In a statement of her own, Clinton said she was "honored" to receive the endorsement.

“We need to take immediate action to make America the clean energy superpower of the 21st century, create good-paying jobs, and make sure no one is left out or left behind, from communities struggling with the legacy of environmental racism to the coalfield communities that kept America’s lights on for generations.”