Rebuffing a request from 17 Republican Senators, a group of government watchdog groups has declined calls to push for a Senate Ethics Committee investigation into allegations that Democrats mixed politics with policy in a recent spat over terrorism reinsurance legislation.

Instead, eight leading watchdog groups — which include key individuals who span the ideological spectrum — wrote Senate Republican Conference Chairman Rick Santorum (R-Pa.), daring Republicans themselves to call for the chamber’s investigative arm to look into the matter.

“As members of the Senate you are free …to bring this matter to the attention of the Senate Ethics Committee,” the groups wrote last week. “As you know, the ethics panel, unlike our groups, has the power to subpoena information.”

The watchdog groups also noted that Sen. Larry Craig (R-Idaho) — one of the Senators who had called on the groups to investigate — is a member of the Ethics panel and “is therefore in a position to raise this matter directly with his colleagues on the panel.”

The letter was signed by the Campaign Legal Center, the Center for Responsibility and Ethics in Washington, Center for Responsive Politics, Common Cause, Democracy 21, Judicial Watch, Public Campaign and Public Citizen.

The response from the watchdog groups comes less than a month after Santorum and 16 of his GOP colleagues prodded the outside organizations to call for an investigation into allegations that Democrats on the Banking, Housing and Urban Affairs Committee decided to drag their feet on a bill to extend terrorism risk insurance after lobbyists for the insurance industry agreed to host a fundraiser for the GOP opponent of Minority Leader Tom Daschle (D-S.D.).

The decision by the Democrats to shift tactics on the industry-backed terrorism reinsurance bill was first reported in Roll Call last month.

In a letter to the groups, the GOP Senators had said: “As non-partisan watchdogs of Congress, we are confident that your organizations are dismayed at such an explicit link between legislative activity and political contributions.” The Republicans urged the groups to pursue the case with the same intensity that they have pursued ethics complaints against Republican lawmakers such as House Majority Leader Tom DeLay (Texas).

“It is our hope that you intend to aggressively respond to this situation, just as you have so faithfully pursued actions against Members of Congress for more obtuse breeches of the relationship between politics and public officials,” the GOP letter said.

However, in their reply to the Republicans, the groups said that they take such matters to House and Senate ethics committees “only when we believe that sufficient public information is available to raise serious questions about whether a violation of House or Senate ethics rules has occurred.”

They continued: “In this instance, the only public information you point to as the basis for alleging a possible Senate ethics violation is a single anonymous reference to an anonymous Senator in a Roll Call story.”