The campaign is a bid by Steyer -- who has not ruled out a run for office himself -- to "demand that elected officials take a stand" on an issue Democratic leaders have so far largely avoided.
"A Republican Congress once impeached a president for far less. And today, people in Congress and his own administration know that this President is a clear and present danger who is mentally unstable and armed with nuclear weapons," Steyer says in the ad, which largely features him speaking directly to the camera.
The ads are running on broadcast stations in New York and California and nationally on cable television. Accompanying the TV ads is what a Steyer aide said is a seven-figure digital ad buy intended to get the minute-long spot a large audience online.
Steyer is paying for the ads himself, and they are not part of his NextGen America political apparatus.
Instead, the ads point to a new website -- NeedToImpeach.com -- which features an open letter where Steyer takes clear aim at California Sen. Dianne Feinstein, citing -- without using her name -- Feinstein's comment that Trump "can be a good President." Feinstein has since downplayed the comment.
In the letter, Steyer hits Trump for ending protections for undocumented immigrants brought into the United States as children, for "actively sabotaging" Obamacare, and for "repealing clean air protections and unleashing polluters."
"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. These actions represent systemic attacks on our nation's future," Steyer writes.
Steyer is openly mulling a run in California's primary against Feinstein next year. State Senate Democratic leader Kevin de León has already entered that race, challenging Feinstein from the left. Steyer has also considered running for California governor in 2018 or president in 2020.
Most Democrats have not yet publicly broached the subject of impeachment -- though Reps. Al Green of Texas and Brad Sherman of California have each introduced articles of impeachment in the House, and Rep. Steve Cohen of Tennessee plans to do so.
Former White House chief strategist Steve Bannon warned Trump about the 25th Amendment, which allows a majority of the Cabinet to vote to remove a sitting president, Vanity Fair recently reported