WASHINGTON – DFL state Sen. Terri Bonoff is leaving the Legislature to challenge Republican U.S. Rep. Erik Paulsen, according to high-ranking Democratic sources in Minnesota and Washington.

Bonoff's team is planning to launch her campaign Saturday at the local Senate convention. The Minnetonka senator has been in state office since 2005.

Self-described as a moderate, Bonoff is a former business executive who says her private-sector experience has helped her win over Republicans on several key union and fiscal issues. She bucked her party last year when she sponsored a measure that would end seniority-guided layoffs for public school teachers, a law currently being challenged in Minnesota courts after the bill died last year. Bonoff has also voted against raising taxes on high earners.

The Third Congressional District spans parts of the Twin Cities' northern and western suburbs, including Brooklyn Park, Minnetonka, Eden Prairie and even Bloomington — including the Mall of America.

Voters there have solidly supported Paulsen since 2008, but have also voted to elect President Obama twice and Democratic Sen. Amy Klobuchar. Democrats consider the Third District a swing district — particularly in a year where Republicans could be hurt by Donald Trump's name at the top of the ticket this November.

For years, state Democrats say they have tried to convince Bonoff to run against Paulsen.

"She's a true moderate," said state Sen. Melisa Franzen, DFL-Edina. "She's a well-known person in the Legislature, and her district. She's very competitive and certainly a stellar fundraiser, so watch out."

Franzen highlighted Bonoff's work on higher-education issues, saying she has worked on efforts to develop the state's workforce.

"She stands for what she believes in, and sometimes it's not the popular decision, but she's a strong advocate for the issues that she cares about, and she's very effective," Franzen said. "She'll do great work at a higher level."

A young, state-based lobbyist named Jon Tollefson had already filed paperwork to run against Paulsen and raised $86,000 in the first quarter of this year in the effort, but he is expected to drop out Saturday and throw his support behind Bonoff.

Bonoff, 58, grew up in Edina and later attended Clark University in Worcester, Mass. She spent 18 years in business before leaving to spend more time with her four children and husband. Before being elected to the Senate, Bonoff served on the Minnetonka Planning Commission and as a volunteer for the Hopkins Legislative Action Commission.

Bonoff ran for the congressional seat in 2008, the last time it was open, but ultimately lost the DFL endorsement. Paulsen was first elected to Congress that year.

Paulsen already holds colossal fundraising advantages. He is on the House Ways and Means Committee, which is charged with tax regulation and had more than $2.3 million in his campaign coffers, according to federal election reports filed on Friday. He raised more than $500,000 in the first quarter of this year.

Despite one of the most conservative voting records in the Minnesota delegation, Paulsen steers clear of controversial hot-button topics and is generally a soft-spoken Republican on Capitol Hill. He touts his support for lowering taxes, small businesses and has been prominent in fighting against human trafficking.

Since being elected, Paulsen has said his single biggest accomplishment was repealing the medical device tax — a measure that Obama didn't support but ultimately signed in a broader budget agreement.

The repeal was a major boon to the industry, which rewarded Paulsen handsomely in campaign contributions. Minnesota is second only to California in the number of people — some 35,000 — working in medical technology at more than 700 companies and Paulsen has raised almost $100,000 alone from medical device companies.

Asked about the specter of Paulsen's political threats this year, National Republican Congressional Committee Chairman Rep. Greg Walden, R-Ore., said on Friday he wasn't concerned.

"Erik is a good member, he's raising a lot of money," Walden said. "He's capable of raising a lot more. He does his business. I think he'll take care of it. I'm not panicked over that one at all."

Reached for comment, Bonoff declined, saying she would announce plans Saturday.

allison.sherry@startribune.com 202-383-6120