They've got muck; we've got rakes. TPM Muckraker
You can see the letter here.
A spokesman for the House Select Committee on Energy Independence and Global Warming, which is probing the forged letters, told the Washington Post: "We have confirmed [that the letter is fake] directly with the person whose name was forged."
A spokeswoman for the coal group on whose behalf Bonner was working, the American Coalition for Clean Coal Electricity, told the Post that it had brought the letter to the committee's attention, but that it couldn't confirm that the letter was forged, even after talking to the person whose signature is on it!
Bonner has blamed the forged letters on a temporary employee.
Late Update: Charles Santrock, the American Legion official whose name is on the letter, tells TPMmuckraker that he never signed on to ACCCE campaign, or spoke with anyone about the issue. He adds that the signature on the letter, which he was shown by congressional investigators, does not match his signature.