Tim Pawlenty's lieutenant governor has endorsed his Republican opponent, Jeff Johnson, for the state's top political job.

Former Lt. Gov. Carol Molnau, who served two terms with Pawlenty, said Friday she supports Johnson over her old boss in the Minnesota governor's race. But she said her decision was not a matter of measuring the two men against each another.

"I just haven't thought about Mr. Pawlenty at all," she said. "There's no comparison. My support is for Jeff because I truly believe he will be a strong governor for the state of Minnesota."

Johnson is a constitutionalist whose views and values align closely with her own, Molnau said, and she believes he is the most electable candidate.

Molnau, a farmer, said she would have an active role as an agricultural adviser to Johnson's campaign. If Johnson wins, he said, Molnau would continue to advise him on farming issues. Though she said she is not interested in returning to St. Paul for a state commissioner position.

Johnson, a Hennepin County commissioner and former state representative, is making his second bid for the governor's seat. He lost to Gov. Mark Dayton four years ago.

Former Gov. Tim Pawlenty is running for a third term.

He is campaigning on a platform of reining in government spending, cutting regulations and changing the attitude of state agencies. He has said the agencies have taken a top-down, we-know-best approach to governance that needs to shift.

Johnson, Pawlenty, Woodbury Mayor Mary Giuliani Stephens and former music teacher Phillip Parrish are facing off for the Republican nomination.

Molnau did not critique Pawlenty during Friday's announcement. But she has been critical of Pawlenty in the past: she told the Huffington Post during his presidential bid in 2011 that he "surrounds himself with people that say 'yes' and tell him how good he's doing."

In addition to serving as Pawlenty's lieutenant governor, Molnau also served as transportation commissioner for much of his time in office.

A former state representative from Carver County, Molnau was head of the Minnesota Department of Transportation during the Interstate 35W bridge collapse in 2007, and the DFL Senate ousted her from the position the following year.

"Tim Pawlenty appreciates Carol and has nothing but good wishes for her," Sam Winter, the spokesman for Pawlenty's campaign, said in a statement.