Daschle, Clark said in an e-mail sent Tuesday to "loyal supporters," is "The No. 1 target of virtually every conservative organization in America."
"He's in for a tough fight," Clark said, alleging that senior White House aide Karl Rove "has already sent several of his operatives to work to defeat Tom."
"I'm going to be helping Tom as much as I can," said Clark, who pledged to campaign throughout South Dakota with Daschle during August.
Clark, who claimed to have been a Republican prior to his entry into the 2004 Democrat primaries, asked his supporters to give money to Daschle's re-election campaign so they could, "Send a message to George Bush and Karl Rove by contributing $50 to Tom's campaign right now."
"Show the Republicans the depth and breadth of Tom Daschle's grassroots support," Clark urged in the e-mail.
Daschle's GOP opponent in November, former U.S. Rep. John Thune, is making his second bid for the U.S. Senate, having lost a 2002 race to U.S. Sen. Tim Johnson, D-S.D., by 524 votes.