Senate Republicans’ slate of candidates this November could have a significant business flavor.

Self-funded businessmen are surging in three key GOP primaries right now in Arizona, Missouri and Wisconsin, and all three appear to have a good shot next month of beating better-known Republicans who have held high-level elected offices.

St. Louis area manufacturing executive John Brunner meets with supporters after announcing his candidacy for U.S. Senate, Oct. 3, 2011, in St. Charles, Mo. Brunner is one of a few Republican businessmen who could win their party’s Senate nomination this fall. (Jeff Roberson — Associated Press)

To wit:

* In Wisconsin, hedge fund manager Eric Hovde led four-term former governor Tommy Thompson 31 percent to 29 percent in a poll by Democratic-leaning automated pollster Public Policy Polling this week. And he was narrowing the gap but trailed by 12 points in a new Marquette University poll Wednesday.

* In Missouri, manufacturing executive John Brunner released a poll a couple weeks back showing him up by 20 points on former state treasurer Sarah Steelman and Rep. Todd Akin. (Other polling has shown a closer race.)

* And in Arizona, real estate investor Wil Cardon is giving Rep. Jeff Flake a significant scare in his primary, where a PPP poll from May showed him cutting a 49-point lead down to 22 points. (It seems logical that the gap has closed even more since then, given Cardon’s heavy presence on TV, and the fact that Flake and his allies are now going after him.)

All three men have never held or run for elective office before, which would make them rarities in the Senate. (Republicans also have busi­ness­peo­ple running in primaries in Connecticut and Michigan, but both races are lower-tier targets.)

Over the last four elections, only six senators have been elected without previously holding some kind of elected position. And just one of them — Sen. Ron Johnson (R-Wis.) — came directly from the business world. Two others previously held cabinet posts; one was a doctor; one was a lawyer; and one was a comedian/political commentator (wonder who THAT was!).

In many ways, it’s not surprising to see busi­ness­peo­ple step up to run and have some success. There is a significant anti-incumbent and anti-Washington sentiment out there right now, and it’s already led more outsiders to be elected to the House and Senate. In 2010, Johnson was one of three senators elected to their first elective office — the others were Sens. Mike Lee (R-Utah) and Rand Paul (R-Ky.) — and about 40 percent of House freshmen had never been elected before.

In addition, economic tough times have put a premium on the kind of fiscal know-how that a businessperson can lay claim to.

But it’s a lot easier to make your way into the House that way; running a Senate campaign is a huge undertaking in which a previously private life is suddenly splayed open for the public to dissect, in a much bigger way than at the House level.

When it comes to busi­ness­peo­ple running for office, there has traditionally been an arc. Early on, their business experience gives them a leg up over better-known opponents. This goes double — or triple — when they can self-fund millions for their campaign (as Hovde, Brunner and Cardon have done) and have a more sustained advertising presence than their opponents (also true of all three).

But often, their lack of political experience and vetting can catch up to them. As these three candidates climb in the polls and as the primaries creep closer (all three are in August), there will be plenty of scrutiny, and their more politically experienced opponents won’t stand idly by, and let the newbie take over.

Oftentimes, this can lead a political outsider to lose his or her early momentum. And in all three cases, these businessmen have begun weathering attacks in the last few days — Hovde for having spent decades in D.C. (though not in elective office), Brunner for failing to pay taxes on his plane and giving money to “an extreme animal rights group,” and Cardon for his business’s hiring of illegal immigrants.

Despite these candidates’ outsider credentials, two of them (Hovde and Cardon) also face opposition from the outsider-friendly conservative Club for Growth and other right-leaning groups. The Club and some tea party groups are backing Flake in Arizona and former congressman Mark Neumann in Wisconsin. So even as they’re outspending their opponents by wide margins early on, they will face attack ads in the weeks ahead, and potentially a lot of them.

Brunner could be the exception to this rule, given the fact that outside groups have shied from taking sides in the primary to face Sen. Claire McCaskill (D-Mo.). In addition, Steelman’s campaign is short on cash, and the one candidate with a big advertising budget — Akin — has shown little desire to go negative on Brunner.

As Mitt Romney’s presidential campaign has shown, a lengthy and successful business career can be a great asset on its surface, but as with a voting record, that’s always something for opponents to mine.

Where Hovde, Brunner and Cardon seem to differ from past outsiders running for Senate is that they’ve surrounded themselves with well-regarded, well-known and smart campaign teams that can guide them through those pitfalls.

And all three are looking like serious contenders in some very high-profile races.