Raising the stakes in the battles with his Democratic counterpart, Senate Majority Leader Bill Frist (Tenn.) plans to campaign next month in Minority Leader Tom Daschle’s home state of South Dakota on behalf of GOP candidate John Thune.

Tentatively slated for May 22, Frist is expected to attend a campaign rally and a fundraiser for Thune, the former three-term House Member who is giving Daschle his toughest Senate race since winning the seat in 1986.

While Frist has helped Thune at fundraising events in Washington, the May trip marks his first foray into Daschle’s home territory, an unusual campaign swing for one Senate floor leader against the other leader.

Thune’s campaign said there was no reluctance by Frist to campaign in Daschle’s political backyard. “None at all. Frist has already been helpful on several fronts,” said Dick Wadhams, Thune’s campaign manager. “There’s certainly no hesitation that I’m aware of.”

Frist is also slated to attend a Lincoln Day dinner in Rapid City for a county GOP.

Wadhams said the sheer nature of the race being the highest-profile Senate campaign of this cycle is drawing Frist out to South Dakota, something a Frist aide privately confirmed.

“I don’t think it’s any big surprise that he would come to South Dakota to campaign for John,” Wadhams said, suggesting this could be the first of several stops in Daschle’s state for Frist. “We’ve got this one in May, and I assume there’s a good chance he’ll come back.”

Frist is already very familiar with South Dakota and Thune, who lost to Sen. Tim Johnson (D) by 524 votes, the only real disappointment Frist suffered on election night 2002 as chairman of the National Republican Senatorial Committee that cycle.

Daschle learned of the Frist trip to South Dakota a few weeks ago, and responded by inviting the GOP leader to tour an Air Force base. Dan Pfeiffer, Daschle’s spokesman, said the Senator was still awaiting word from Frist regarding the visit to the base, which residents fear may get closed.

“He welcomes him to South Dakota, and hopes he comes often,” Pfeiffer said, noting that Daschle intends to lobby Frist on local issues such as country-of-origin labeling for meat.

Senate Historian Richard Baker could not recall a time in the modern era of campaigns when one floor leader campaigned against the other in his home state, mostly because Daschle is the first floor leader since the 1960s to face a tough re-election fight.

In 1962 and 1968, then-Republican leader Everett Dirksen (Ill.) faced tough campaigns, winning with 53 percent of the vote each time. Dirksen enjoyed a very cordial relationship with the Democratic leader at the time, Mike Mansfield (Mont.).

The last Senate floor leader to lose his re-election was Ernest McFarland (D-Ariz.), who was defeated in 1952 by Barry Goldwater (R).

How Frist’s open campaigning in South Dakota will affect his personal relationship with Daschle back in D.C. remains to be seen.

Daschle has admitted in interviews that it took some time to adjust to the different style of Frist from his predecessor, Sen. Trent Lott (R-Miss.). While Lott would barge into Daschle’s office or call him up on his direct number, Frist is prone to sending BlackBerry messages.

And Daschle has been the single biggest thorn in Frist’s legislative side, leading Democratic filibusters throughout the 108th Congress on numerous bills and nominations.

At the close of last year’s session, Daschle’s top deputy, Minority Whip Harry Reid (D-Nev.), told reporters that Frist was demonstrating “rank amateur” leadership.

But there are signs that the two leaders have grown more comfortable together, and they had planned an unannounced trip together to Iraq that was supposed to happen this week as a show of bipartisan support for the troops. The trip was canceled late last week when the situation in Iraq turned dire, making it impossible for them to travel there unless they had hundreds of soldiers working to protect them.

They plan to make the trip together at a later date.

Daschle is already smashing all fundraising records for South Dakota Senate races. By the end of December, he had taken in more than $7.2 million for the 2004 election cycle and had spent more than $4.9 million. Daschle told Roll Call last year his fundraising goal was “well over $10 million.”

To defeat Thune in 2002, Johnson raised and spent $6.8 million.