MADISON, Wis. (AP) -- U.S. Sen. Rand Paul has endorsed Mark Neumann in the race for Wisconsin's open Senate seat.

Rand Paul is the son of U.S. Rep. Ron Paul and a member of the Senate's Tea Party caucus. He says he believes Neumann, a former congressman, is the most conservative candidate in the race and will push back against government spending and tax increases.

The national conservative group Club for Growth's political action committee endorsed Neumann in September, saying Neumann is a fiscal conservative and will lead the fight for limited government.

The seat is open due to the retirement of Democrat Herb Kohl. Neumann, former Wisconsin Gov. Tommy Thompson and state Assembly Speaker Jeff Fitzgerald are all vying for the Republican nomination.