In 2006 the 21st state senate district was again an open seat, Lehman ran and defeated Republican Bill McReynolds.

"[7] On June 6, 2012, Lehman narrowly defeated Wangaard, giving Democrats a brief one vote majority in the Wisconsin State Senate.

On November 18, 2013, Lehman announced that he would not seek re-election, and instead launched a campaign for Lieutenant Governor in the 2014 Wisconsin gubernatorial election.

Lehman and his running-mate, gubernatorial candidate Mary Burke, lost the general election to incumbents Scott Walker and Rebecca Kleefisch.

[9] Lehman was defeated by Racine Unified School Board President Robert Wittke in the 2018 general election.