People protesting against the global climate crisis on September 20, 2019 in New York City. Photo: Spencer Platt/Getty Images

More than 170 of the world's most esteemed environmental activists signed on to an open letter on Monday urging their supporters to vote for Joe Biden rather than vote for the Green Party or sit out the election, The Daily Beast reports.

The big picture: The group says "progressives who vote for the Green Party candidate, or write in Henry David Thoreau, or refuse to vote at all" will help win the election for Trump, whom they excoriated for his "unprecedented malignancy, fear mongering, pathological lying, and atrocious policymaking."

  • Flashback: Trump won in Michigan, Wisconsin and Pennsylvania in 2016 by smaller margins than the total votes cast for Green Party nominee Jill Stein in each state, The Daily Beast notes.
  • Signatories to the letter include the likes of Earth Day founder Denis Hayes and Environmental Action coordinator Peter Harnick.

What they're saying: “Angry right-wing voters and liberal absentees put Trump in the White House in 2016. In 2020 the same unholy team could keep him there," the letter reads.

"Sure, [Biden] isn’t perfect. Which of us is? But in the 2020 election, the most crucial since 1865, we have only two meaningful options. We can make a lifetime humanitarian our president, backed by an able cabinet and a progressive Congress; or expand the strongman rule of Donald Trump, who desecrates his office every day, spreads racism and a fatal virus for political gain, ignores environmental justice, embraces the fossil fuel industry, and calls the climate crisis a hoax."

Read the full letter.

Go deeper: Why Biden and the Democrats went big on climate

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The top Republicans who aren't voting for Trump in 2020

Photo: Brendan Smialowski/AFP via Getty Images

Former Pennsylvania Gov. Tom Ridge announced in an op-ed Sunday that he would be voting for Joe Biden.

Why it matters: Ridge, who was also the first secretary of homeland security under George W. Bush, joins other prominent Republicans who have publicly said they will either not vote for Trump's re-election this November or will back Biden.

Former GOP governor of Pennsylvania Tom Ridge endorses Joe Biden

Photo by Drew Angerer/Getty Images

Tom Ridge, the former Republican governor of Pennsylvania, will vote for Joe Biden, he announced in a Philadelphia Inquirer op-ed on Sunday.

Why it matters: Ridge, who also served under George W. Bush as the first secretary of Homeland Security, said this would be his first time casting a vote for a Democratic candidate for president. He's now the third Republican former governor from a swing state to endorse Biden and reject Trump — joining John Kasich from Ohio and Rick Snyder from Michigan.

Manchin says he will oppose expanding Supreme Court if Democrats win Senate

Sen. Joe Manchin (D-W.V.) would oppose any move to expand the number of justices on the Supreme Court if Democrats win back the Senate and White House in the election, he told Jake Tapper on CNN's "State of the Union" Sunday.

Driving the news: Democrats have floated adding more justices to the court as retaliation for Republicans rushing through a new justice for President Trump weeks before the 2020 election, after stalling President Obama's final nominee nine months before the 2016 election.