On Friday morning, President Trump sent out a Twitter post slamming Tom Steyer, a billionaire environmentalist and Democrat mega-donor who just launched a $10 million television ad campaign against the president, calling for his impeachment.

Steyer had already spent $90 million trying to elect Democrat candidates and stop Trump during the 2016 election season, only to see Donald Trump win the presidency and Republicans win control of both the House and the Senate.

“Wacky & totally unhinged Tom Steyer, who has been fighting me and my Make America Great Again agenda from beginning, never wins elections!” Trump tweeted.

It didn’t take long for Steyer to shoot back with a string of tweets directed at the president.

“You’re right about one thing, Mr. Trump,” he tweeted, adding, “I have been fighting your racism and corporate groveling from the beginning—and always will. Americans deserve much better.”

“Americans across the board know you’re a danger to the people of this country. @NancyPelosi @SenSchumer it’s time to take a stand,” he challenged.

Then, calling on people to sign his impeachment petition, Steyer added, “Hundreds of thousands of Americans are adding their voices to the movement to impeach this President. It’s only a matter of time until he is gone. Sign our petition today and tell Congress to impeach President Trump.”

Later Friday, MSNBC producer Kyle Griffin posted a message to GOP Sen. Lindsey Graham, saying, “If Republicans don’t pass tax reform, Democrats will take back the House and attempt to impeach Trump.”

At this, Steyer shot out another warning, claiming that “Trump has already committed impeachable offenses,” and adding, “Time to impeach is now.”

Steyer has his TV ad campaign video pinned to the top of his Twitter page presently. In it, he claims that “this president is a clear and present danger who is mentally unstable and armed with nuclear weapons.”

He is said to be pouring $10 million into the effort.