With just five days to go, the GOP Senate primary in Utah between businessman Tim Bridgewater and lawyer Mike Lee is getting nasty — at least by Beehive State standards.

That’s because the winner is all but certain to win the general election this fall, and Bridgewater and Lee have only ramped up their attack machines since they toppled Sen. Bob Bennett at the state GOP convention in May.

Lee’s campaign has challenged Bridgewater’s conservative credentials by insisting that his business interests were built with government earmarks and stimulus money. Some Lee backers are also drawing connections between Bridgewater and a controversial mailer that was distributed in the days before the convention that used a picture of Lee and the Mormon Temple. Lee’s camp has already said it will file a Federal Election Commission complaint over the mailer and has asked Bridgewater to help him get to the bottom of who paid for it.

Meanwhile, Bridgewater launched his first ad of the primary this week and attacked Lee with a message that the last thing Washington, D.C., needs now is another lawyer who will join the club.

“For too long Washington has been run by lawyers and political insiders,” Bridgewater says in the spot. “Let’s take back our country and stop the insanity.”

Lee spokesman Boyd Matheson suggested Wednesday that the last thing Congress needs is another politician who wants to treat government like a growing business.

“If you look at a typical business, they expand and look for new opportunities, and that’s what the government has done,” Matheson said. “We need someone who is going to go in there and use the Constitution and the law to reduce the size and reach and cost and get government out of our business.”

Six weeks after his defeat at the convention, Bennett continues to cast his shadow over the race. The Senator endorsed Bridgewater last week, a move that Lee’s camp said would only redirect the anti-Bennett anger of the convention at Bridgewater. But Bridgewater supporters say Bennett can still bring in votes among the larger primary electorate.

A public opinion poll of rank-and-file Republican primary voters commissioned by the Salt Lake Tribune in early May found Bennett with a 19-point lead over Lee.

Bridgewater media consultant Brian Donahue said Bennett’s endorsement, combined with that of the convention’s fourth-place finisher, conservative activist Cherilyn Eagar, illustrates that Bridgewater can represent a large swath of voters from across the state.

“Tim Bridgewater is carrying the banner for a new kind of Republican that many types of frustrated voters and Republicans can rally behind,” Donahue said.

But Matt Hoskins, a spokesman for Sen. Jim DeMint’s Senate Conservatives Fund political action committee, disagreed. The South Carolina Republican is backing Lee.

“Bennett’s endorsement clarified that Bridgewater is Bennett-light and that he is the establishment candidate in the primary,” Hoskins said.

After tea party activists played a role in knocking off Bennett at the convention, both Lee and Bridgewater have sought to rally support from those groups, and both have found success. But late in the campaign, Lee, who was a clerk for Supreme Court Justice Samuel Alito, has also found a receptive audience with the libertarian and constitutionalist crowd.

This week he earned a high-profile endorsement from libertarian champion Rep. Ron Paul (R-Texas).

“The tea party is definitely split,” Bridgewater spokeswoman Tiffany Gunnerson said. The “Ron Paul constitutionalist movement, I would give the edge to Mike Lee on that.”

But, Gunnerson added, that group will make up a much smaller portion of the primary electorate than it did at the convention, which tends to draw more hard-core party activists.

Although polls have been all over the map, most Utah political insiders are predicting a close race Tuesday.

Bridgewater turned in a surprisingly strong showing at the May 8 convention by taking first place by a 15-point margin. He beat Lee 57 percent to 42 percent and came 3 points shy of winning the nomination outright under convention rules.

But with big-name national endorsements, including from DeMint, Lee’s camp has claimed momentum since the convention.

After going on television in early June — a week and a half before Bridgewater was on the air — Lee’s camp conducted a poll June 8 that showed Lee ahead by 9 points, with 31 percent of voters undecided.

One Bridgewater operative disputed those numbers Wednesday, noting that internal campaign polling showed Bridgewater up by 9 or 10 points coming out of the convention. The operative acknowledged that Lee’s early television push helped him close that gap to about 4 points as of last week but said that Bridgewater is still ahead.

Fundraising reports from early June showed Bridgewater with at least $100,000 more in the bank for the final three weeks, but Lee has proved over the course of the campaign to be the better fundraiser.

Bridgewater has mostly self-funded his campaign with nearly $400,000 in personal loans. Lee has raised at least $200,000 more from individual contributors than Bridgewater. Lee’s camp believes that voters who are willing to cut checks are more likely to show up for what is expected to be a low-turnout election Tuesday.

But the Bridgewater operative said Lee shouldn’t take all the credit for his fundraising.

“When it comes to fundraising, [DeMint] has been golden for Mike,” the consultant said.

DeMint’s Senate Conservatives Fund has bundled more than $100,000 to Lee since DeMint endorsed him at the convention. The SCF has also spent more than $75,000 in independent expenditures on the primary to benefit Lee.