MILWAUKEE — Billionaire liberal activist Tom Steyer is in Wisconsin meeting with college students as he works to topple Republican Gov. Scott Walker and House Speaker Paul Ryan.

Steyer's visit to the state led Walker to call him "extreme" in a tweet, saying he was "pushing impeachment" and a "Far-Left agenda."

Steyer told the Milwaukee Journal Sentinel on Tuesday that Walker and Republicans in Wisconsin "are nervous about the fact that they've done such a bad job."

Steyer is an environmental activist from California who spent more than $90 million on Democratic and liberal causes in the 2016 campaign. Through his youth organizing group NextGen Rising, Steyer plans to spend $30 million in 10 states, including Wisconsin, to help Democrats win this year.

Steyer visited Marquette University and the University of Wisconsin-Madison.