Amidst an outcry from Senate Democrats, Majority Leader Bill Frist (R-Tenn.) has proclaimed former Rep. John Thune’s bid to oust Minority Leader Tom Daschle (D-S.D.) a “race of national importance” that GOP donors should consider their top priority.

In the latest indication that Frist will personally campaign against his Democratic counterpart, the Republican leader signed a two-page fundraising letter last week for Thune that was sent to thousands of potential donors. The letter was a clear call to arms on behalf of the former three-term House Member who is trying to oust Daschle, a three-term Democrat.

“If you can only make one more contribution to one of our Republican Senate candidates this election cycle … you should make that gift to John Thune,” Frist proclaimed in the letter. To add emphasis, that phrase was set in bold-faced capital letters, accompanied by an exclamation point.

The direct-mail pitch is the latest step in Frist’s escalating battle to oust his Democratic counterpart, the first Senate floor leader to face a tight re-election battle in almost 40 years.

As of March 31, Daschle had $5 million in cash on hand and led in polls by about a half-dozen points. Thune had $1.9 million in the bank.

While Daschle has not spoken publicly about Frist’s efforts against him, his top deputies say the Majority Leader has ruptured the decorum that has historically existed between the chamber’s two leaders. “This breaks all Senate tradition. You have to have leaders work together for the good of the Senate,” said Minority Whip Harry Reid (D-Nev.). “If they can’t work together, the place falls apart.”

“It cannot help the relationship,” said Sen. Dick Durbin (D-Ill.), an Assistant Floor Leader appointed by Daschle.

Frist said Tuesday that his relationship with Daschle is fine and that the two continue to speak on a regular basis, including discussions about Frist’s campaign efforts for Thune. “We continue our conversations, which remain confidential,” Frist said.

However, the Majority Leader indicated he wasn’t certain that he had fully read the letter and signed off on its contents before it was mailed on Thune’s behalf. “I need to go and look at the letter and see if I’ve seen it,” he said.

Frist did not disavow the letter, however, and his aides and other Senators said Daschle’s supporters were painting their candidate as a victim in a bid to inoculate him from attack. “It’s a standard fundraising letter — Daschle should be familiar with it,” said Frist spokesman Bob Stevenson.

Sen. Rick Santorum (Pa.), the chairman of the Republican Conference, accused Daschle’s camp of creating a “false outrage factor” at Frist’s efforts for Thune. Santorum said Daschle and his fellow Senate Democrats already destroyed the chamber’s traditions through the use of filibusters to block judicial nominees and other acts of alleged obstruction, leaving the Senate at a legislative standstill for much of this year.

“Any line that has ever been laid in the Senate, Senator Daschle has crossed over,” Santorum said.

The letter follows a barrage of assistance Frist has been giving Thune. Thune was first recruited into a Senate race in 2002 when Frist was chairing the National Republican Senatorial Committee. Thune lost that race to Sen. Tim Johnson (D-S.D.) by 524 votes in a campaign that was widely viewed as a proxy race for control of the Senate.

Now, as Majority Leader, Frist’s actions to support Thune appear to be turning Daschle’s race into a personal battle between the two floor leaders. Within days of Thune’s announcement of his intention to run Jan. 5. Frist began rounding up checks for Thune. The donations began piling up even before Thune had an account to deposit them in.

In the first quarter, Frist bundled $156,000 in contributions from supporters. His leadership political action committee, Volunteer PAC, gave another $10,000 to the Thune campaign — the maximum allowed by law.

Last weekend in Nashville, at Frist’s annual major political event for Volunteer PAC, Thune was one of a handful of nonincumbents to be featured. Some of the money from that event will come on top of the donations Frist has already steered to Thune, according to Frist and Thune aides.

In a move that has particularly irked allies of Daschle, Frist will stump for Thune in South Dakota on May 22, marking the first time a leader has campaigned against the other party leader on his home turf in perhaps a century.

“Senator Daschle would never consider going to Tennessee,” Reid said.

Frist’s supporters say the Majority Leader is just being honest in his open support of Thune, rather than doing everything he can behind the scenes to oust Daschle.

Thune’s campaign manager, Dick Wadhams, said Frist’s help is but a drop in the bucket compared to the more than $10 million Daschle has already raised for the race — $5 million of which he spent in the previous 15 months. The Frist letter — which was a cover sheet for a four-page missive from Thune accusing Daschle of ties to “radical liberal special interest” groups such as NARAL Pro-Choice America — was sent to “various Republican contributor lists,” Wadhams said. It was paid for by John Thune for Senate.

Wadhams dismissed the complaints from Reid and Durbin as an attempt to sidestep Daschle’s attempts to block President Bush’s agenda in the Senate. “They’re all co-conspirators in the continuing effort for Daschle to claim victimhood,” Wadhams said.