Sen. Tom Coburn (R-Okla.) has just gained some very important allies in his bid to investigate the Coconut Road earmark buried in the highway technical corrections bill, according to a Republican aide.

Sens. John McCain (R-Ariz.) and Barack Obama (D-Ill.) plan to sign on to the Coburn plan, which would launch an investigation into which lawmaker is behind the earmark for a highway project near Fort Myers, Fla.

The Senate passed a motion to proceed to the highway bill, 93-1, Monday night, but it has yet to reach the floor because of concerns about the Coburn amendment.

The bill’s floor manager, Sen. Barbara Boxer (D-Calif.), thinks the matter should be taken up by the Ethics Committee, which she also chairs. But the problem with that is many people believe the author is ex-House Transportation and Infrastructure Chairman Don Young (R-Alaska), and there is no procedure for an ethics committee to investigate a Member of the other chamber.

The Coburn amendment would establish a bipartisan panel selected by Speaker Nancy Pelosi (D-Calif.), House Minority Leader John Boehner (R-Ohio), Senate Majority Leader Harry Reid (D-Nev.) and Senate Minority Leader Mitch McConnell (R-Ky.). The panel would investigate who is responsible for the earmark and how it got into the bill and report its findings.

However, the panel would not have any authority to issue or enforce any penalties against the parties involved. The committee would only be able to report to Congress and submit its conclusion to the Senate and House ethics committees.