Steve Welch, a Chester County entrepreneur who built a successful biotechnology company, launched a bid for the Republican nomination for U.S. Senate Thursday, saying the nation needs leaders who "understand the economy from the ground up."

He joins a growing field of at least eight candidates looking to replace Sen. Bob Casey (D., Pa.) by tying the incumbent to President Obama and the nation's economic problems.

"American innovation is strong," Welch, 36, said Thursday in an interview. "I have no concern with our ability to generate ideas, but we're created an environment in which it's more difficult to take ideas and build things, because people in Washington don't have a clue."

A startup founded by Welch in 2001, Mitos, developed equipment that improved the manufacture of vaccines, and grew into a global firm. He sold it to a Fortune 500 company, Parker Hannifin, in 2007, and now is a venture capitalist.

Welch tried to run for Congress in the last cycle, only to be stymied twice by Republican leaders. He announced in 2009 that he would run to replace then-U.S. Rep. Joe Sestak (D., Pa.) in the Seventh District seat, but bowed out when Pat Meehan, the former U.S. attorney and now congressman, got in the race and was endorsed by the GOP establishment.

Then Welch moved into the Sixth District in 2010, hoping to replace U.S. Rep. Jim Gerlach, who was seeking the Republican nomination for governor. That effort stalled when Gerlach instead sought reeelection to the House, embraced by GOP officials worried about losing a seat to the Democrats in a competitive suburban district.

In the web video he used to announce his candidacy Thursday, Welch addressed another potential vulnerability: that he was once a registered Democrat who voted for and donated to Sestak and supported Obama in the 2008 Democratic primary. Welch said he was "so upset" at Republicans' breaking their promises and expanding government that he switched parties.

"I'm the first to tell you I think both parties have failed us over the last decade," he said in the interview. "I'm sure there are some people who will never forgive me for that process. I think the majority of Americans want people in Washington that are free-thinking that are going to vote on their conscience and principle rather than party."

Welch was a registered Democrat from 2006 to 2008, according to registration records, but he said he voted for Republican John McCain for president. He argues that Obama's health care plan and other government regulations have stifled businesses by increasing uncertainty.

"When people don't know what the rules of the road are, they choose not to take the risk," Welch said. He believes lobbyists have "infiltrated" Congress and skewed the tax code, which must be "scrapped" and replaced with a system of lower rates and no deductions.

He faults Casey for voting "98 percent of the time" with Obama.

Casey's party is already portraying the 2012 GOP primary as a race to the right. "This is one of the largest primary fields in the country," said state Democratic Party spokesman Mark Nicastre. "Whoever emerges from the primary will have run far to the right of mainstream Pennsylvania...for the support of the Tea Party."

Tim Burns, a wealthy Washington County software executive who ran unsuccessfully against Democratic Rep. Mark Critz last year in the battle to succeed the late Rep. John Murtha (D., Pa.), declared his candidacy Wednesday.

Tom Smith, a former coal company owner and conservative activist from Armstrong County, got into the race two weeks ago. Mark Scaringi, a former Senate aide and conservative activist from suburban Harrisburg, has been running for more than a year.

David Christian, a decorated Vietnam veteran from Bucks County; tea party leader Laureen Cummings of Scranton; John Kensinger of Bedford County; and retired Army Col. John Vernon of Tioga County also are running. And Sam Rohrer, a former state representative who ran a grassroots campaign against Gov. Corbett in the 2010 GOP primary, has said he is considering a run.

Contact politics writer Thomas Fitzgerald at 215-854-2718 or tfitzgerald@phillynews.com or @tomfitzgerald on Twitter. Read his blog, "The Big Tent," at www.philly.com/BigTent.

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