Galloway's resignation will cause the Republicans to lose their Senate majority. Republicans would hold 16 seats and Democrats would hold 16 seats. It marks a dramatic change from a year ago, when Republicans held a commanding 19-14 majority in the Senate. It was narrowed to 17-16 in August when Democrats gained two seats in recall elections.

The new, 16-16 split will be brief, and one side or the other should take control in May or June, when recall elections are expected to be held for state senators.

Galloway is a big time Tea Party leader here in Wisconsin, according to reporter John Nichols, who spoke about the resignation on Ed Schultz's radio show this morning.