The TV spot will be supplemented by a seven-figure social media buy.

The campaign, which was previewed last week by the New York Times, is not a project of Steyer’s political organization, NextGen America. It is funded directly by Steyer, a donor who has not ruled out a run for office himself and who has built relationships with think tanks and elected Democrats in California and Washington.

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Visitors to Steyer’s new website see a compilation of news articles about Trump’s decisions, and a long open letter from Steyer, with a litany of reasons for politicians to remove Trump from office. Finally, there is an offer to sign up with the campaign.

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“He is repealing clean air protections and unleashing polluters, even as increasingly catastrophic natural disasters supercharged by our warming planet ravaged the country throughout the summer,” Steyer writes. “He has threatened to reduce aid for millions of American citizens in Puerto Rico who are struggling to survive without drinkable water or electricity — a move that would be a total dereliction of his duty. And every day, Americans are left bracing for a Twitter screed that could set off a nuclear war.”

To date, few elected Democrats have called for impeaching the president before the independent investigation headed by Robert S. Mueller III wraps up its work.

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In the House, Reps. Al Green (D-Tex.) and Brad Sherman (D-Calif.), two backbenchers from safe seats, have introduced articles of impeachment with no real hope of being adopted. House Democratic leader Nancy Pelosi, who once fended off liberal demands that her party impeach President George W. Bush, said this summer that Trump might well “self-impeach” as he tumbled from controversy to controversy.

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Republicans, meanwhile, have looked at the impeachment chatter as a potential way to motivate their donors and base. At an August retreat in Wyoming organized by House Speaker Paul D. Ryan (R-Wis.), donors were warned that a Democratic takeover of the House would put Rep. Elijah E. Cummings (D-Md.) in charge of the House Oversight Committee, a perch where he could launch endless investigations with unlimited subpoena power.

But so far, talk about impeachment — or about invoking the 25th Amendment of the Constitution, which would allow the president’s Cabinet to remove him from office — has not been embraced by the Democratic Party’s leaders. Removing Trump after an impeachment in the House would take the votes of 67 senators, leading many Democrats to consider the issue a distraction.