As he mulls a potential 2020 White House bid, Washington Gov. Jay Inslee (D) is taking aim at an unusual target: Sen. Joe Manchin III (D-W.Va.).

In an email to supporters Tuesday, Inslee argued that Manchin, a moderate Democrat, “simply can’t be trusted to make the bold, progressive decisions we need” and should not be allowed to become the ranking Democrat on the Senate Energy and Natural Resources Committee.

“I need your help to stop this,” Inslee said in the email. “Our party must be wholly committed to ending America’s dependence on fossil fuels and building a robust clean energy economy. And Joe Manchin literally shot climate legislation in one of his campaign ads. He supports Donald Trump’s dirty energy agenda.”

The email asked supporters to sign an online petition opposing Manchin’s ascension to the top Democratic spot on the panel. Manchin’s office declined to comment on the petition Wednesday.

Washington Gov. Jay Inslee (D) criticized President Trump's focus on arming teachers on Feb. 26, saying that teachers "don't want to do that." (The Washington Post)

Manchin, who last month won reelection in a state President Trump carried by more than 40 points in 2016, has embraced some of the president’s environmental initiatives and met with him for lunch at the White House on Monday.

Sen. Maria Cantwell (D-Wash.), the current ranking minority-party member on the Energy and Natural Resources Committee, is expected to become the top Democrat on the Commerce Committee in the next Congress, with Manchin poised to take her spot on the energy panel. The development has prompted alarm among liberal and environmental groups who worry the West Virginia Democrat will stymie their climate agenda.

As environmental activists protest in Brussels, the United Nations' climate change talks begin in Poland on Dec. 2. (Reuters)

Some activists are calling for Sen. Bernie Sanders (I-Vt.) to block Manchin by claiming the top minority-partyspot on the energy committee. But Sanders, a potential 2020 contender himself, is expected to remain in his spot as the top Democrat on the budget committee instead.

Jamal Raad, Inslee’s political spokesman, said Wednesday that the governor is not backing a specific candidate for the energy spot and that while the choice is up to Senate Democrats, he strongly opposes Manchin.

“Senate Democrats have a large caucus with dozens of members who understand the task at hand,” Raad said. “We’ll leave the internal deliberations up to them. We just know that Senator Manchin is not one of them.”

Inslee is the outgoing chairman of the Democratic Governors Association, a perch that has allowed him to take his message on the road in anticipation of a potential 2020 bid. A former House member, he won election as governor in 2012 and again in 2016 and has made battling climate change a central part of his platform.

In an interview with the Seattle Times last month, Inslee did not rule out a bid against Trump. He also told the newspaper that the 2020 campaign “should be a referendum on climate change, and we have to have a president who embraces science rather than ignorance.”