Many Republicans, however, believe there is still ill will between him and Gov. Scott Walker from their 2010 gubernatorial primary. Of all the GOP candidates, Neumann might have the most difficult time beating Baldwin in November, at least according to Democrats. One Democratic operative in the Badger State called Neumann "Wisconsin's Sharron Angle," in reference to the Republican who lost to Senate Majority Leader Harry Reid (D-Nev.) last cycle in a race many thought would be a GOP pickup.
Hovde has surprised some with the strength of his campaign, particularly because he spent 24 years living in Washington, D.C., before moving back to Wisconsin just recently to run for office. Hovde has spent millions of dollars of his own money on the campaign, much of it on brutal attack ads linking Thompson to President Barack Obama's health care law.
A poll taken at the beginning of this month by the Marquette University Law School had Thompson at 33 percent, Hovde at 24 percent and Neumann at 21 percent. But a more recent sample from Public Policy Polling, a Democratic-leaning firm, had the race much tighter, with Thompson at 27 percent, Hovde at 25 percent and Neumann at 24 percent. Two GOP sources who had viewed internal polling confirmed that the race is tracking as tightly as the PPP snapshot suggests.
In a last-ditch effort to prove his conservative bonafides, Thompson campaigned Monday with Joe "the Plumber" Wurzelbacher and has been playing up support from Ryan and Walker, even though neither man has endorsed him officially in the race. In the press call Saturday, Thompson called Ryan "a friend" and a partner in policy, "especially on Medicare."
Though it's unclear how high turnout will be, especially after more than 2 million voters turned out for June's recall election, several insiders projected that a higher turnout - 800,000 voters or more - could favor Thompson.
With the Senate in the balance this fall and all eyes on Wisconsin because of Ryan, today's primary is probably only the beginning of one of the nation's most contentious races.
Senate Minority Leader Mitch McConnell, R-Ky., carries a musket on stage as he speaks during the American Conservative Union's Conservative Political Action Conference (CPAC) at National Harbor, Md., on Thursday March 6, 2014.