Illinois businessman Richard Uihlein has now donated a total of $3.5 million toward a super PAC supporting Republican Kevin Nicholson's potential campaign for Wisconsin's U.S. Senate seat.

Uihlein, who is one of the nation's biggest Republican donors, founded the Pleasant Prairie-based Uline company.

He gave $2 million earlier this year to start the super PAC "Solutions for Wisconsin." A spokesman said Uihlein donated another $1.5 million last quarter.

So far, Uihlein is the super PAC's only donor.

Solutions for Wisconsin is focused exclusively on supporting the potential U.S. Senate bid of Kevin Nicholson, a Marine veteran, businessman and former Democrat.

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"I strongly encourage others to support this effort and avoid a repeat of 2012’s divisive Republican primary," Uihlein said in a statement released Wednesday.

Nicholson is one of several Republicans mulling a challenge to Democratic U.S. Sen. Tammy Baldwin in 2018. Others include businessman Eric Hovde, state Senate Majority Leader Scott Fitzgerald, state Sen. Leah Vukmir and state Rep. Dale Kooyenga.

The 2012 GOP primary saw Hovde, former Republican Gov. Tommy Thompson, former U.S. Rep. Mark Neumann and former state Assembly Speaker Jeff Fitzgerald trade jabs for most of the year. Thompson won the primary but lost to Baldwin in the general election.

Democrats seized on news of Uihlein's latest donation.

"It's not surprising that the only person willing to support Kevin Nicholson is an Illinois multimillionaire," said the Democratic Party of Wisconsin in a statement.