In a race where no clear frontrunner has ever emerged, the outcome of today’s Republican Senate primary in Wisconsin may come down to money.

Three credible candidates have been trying to break away from the pack all year. But on the eve of the election it was still unclear who would get to take on two-term Sen. Russ Feingold (D). The answer tonight may determine how competitive Republicans will be against Feingold in the general election. Meanwhile, the three-way Democratic primary to replace retiring Rep. Jerry Kleczka (D) in the 4th district also has proved to be difficult to forecast.

In the Senate contest, early predictions centered on state Sen. Bob Welch, who was the 1994 GOP nominee against Sen. Herb Kohl (D). But Welch has not been able to match his two millionaire opponents in the fundraising department.

Retired auto dealer Russ Darrow and construction company executive Tim Michels have shown a willingness to dig into their own pockets, and both made significant investments on advertising.

Darrow has poured $2.7 million of his personal fortune into the race, while Michels has ponied up more than $1.4 million for his campaign, according to WisPolitics.com.

Darrow and Michels have both spent about $1 million on TV commercials, while Welch has invested significantly less.

The Welch campaign could not confirm how much it has spent on advertising, but estimates range from $50,000 to $100,000.

Those numbers reflect how the entire race has played out, with Darrow and Michels trying to reach out to the broader electorate while Welch has worked hard to shore up the Republican base and play to the grass roots. In Wisconsin, primary voters can select one party’s ballot or another — meaning some Democrats and independents may vote in today’s GOP primary.

But with voters still generally unaware of all four candidates — perennial candidate Robert Lorge is also in the mix — commercials, according to the last public poll, could make the difference.

Whatever puts one candidate over the top, some Republicans, at least privately, are hoping the winner turns out to be Darrow or Michels.

“Republicans feel they have a better shot of making this race competitive if either Darrow or Michels emerges from this primary,” said a knowledgeable GOP source, who did not want to be named.

Besides their business backgrounds — and Michels’ military experience — party insiders like the idea that either Darrow or Michels could hit the ground running financially.

Welch, by contrast, would need a large infusion of outside cash to make a serious run at Feingold, who currently sits atop an almost $3 million war chest.

While the Senate primary gets marquee billing, the Democratic primary in the Milwaukee-based 4th district is expected to produce the city’s next House Member.

Three credible Democrats are vying for their party’s nomination in this overwhelmingly Democratic district.

In the absence of updated polling information, and with three strong candidates competing, most people believe the race to succeed Kleczka is wide open.

“It’s anybody’s call right now,” said Todd Robert Murphy, a GOP consultant who is working for state Sen. Tim Carpenter (D). “It’s a wild card.”

Although his candidate does not have the money of attorney Matt Flynn, a former state Democratic Party chairman, or the outside support of fellow state Sen. Gwen Moore, who is backed by EMILY’s List, Murphy is optimistic that Carpenter can prevail.

“He’s the little engine that can,” Murphy said. “He has an excellent get-out-the-vote effort and saved his money until the end.”

But the Flynn and Moore campaigns are equally bullish.

“We don’t have any [updated] numbers but we certainly are optimistic about the possibility of winning this,” Moore spokeswoman Shelia Payton said.

Payton sought to dispel a theory circulating that black voters will abandon Moore in the primary in favor of GOP candidate Corey Hoze, who is also black.

“There are no signs of black voters moving to the Republican primary,” she said.

Payton also pointed out that the district is heavily Democratic — 66 percent of 4th district voters backed then-Vice President Al Gore in 2000 — and added that the black community is a “large part” of the Democratic base.

In order for Hoze, a former Health and Human Services official, to win in November there would have to be “wholesale [black] defection from the Democratic Party,” Payton said, an outcome she finds highly unlikely.

In the end she said the speculation probably stems from the Hoze campaign, which knows it will have a tougher time beating Moore in November than either Carpenter or Flynn, who are both white.

If either Moore or Hoze wins in November, he or she would be the state’s first black Member of Congress.

For his part, Flynn has relied largely on the old-boys party network.

He is backed by Kleczka and has tapped connections he made during his tenure as party chairman in the early ’80s.

Flynn also is airing a commercial featuring former acting Milwaukee Mayor Marvin Pratt, who is black.

Flynn worked on Pratt’s failed mayoral campaign earlier this year. But the Milwaukee Journal-Sentinel noted that Pratt does not specifically endorse Flynn, he just says “I hold him in high regard.”