WASHINGTON — Sen. John McCain's office denied Thursday that he used the formatting on a letter from the White House as an excuse to delay a vote on Chuck Hagel's nomination for secretary of defense.

"That's absolutely false," McCain's spokesperson Brian Rogers said of the charge, which Democrats had been quietly making on Capitol Hill Thursday.

McCain and Sens. Lindsay Graham and Kelly Ayotte wrote a letter to the White House on Tuesday demanding further information about the September attack on the American consulate in Benghazi, and warned that they would hold a vote on Hagel's nomination pending a response. The White House responded Wednesday — but addressed the letter to Sen. Carl Levin, chair of the Armed Services Committee, and merely CC'ed McCain, Graham and Ayotte.

The White House resent the letter — nearly identical to the first, but for the inverted subject and CC lines — Thursday.

A Senate Democratic aide provided copies of the letters to BuzzFeed. "That is the level of unseriousness we are dealing with here," the aide said.

On the Senate floor earlier Thursday, Reid hinted at the drama.

"Several of my Republican colleagues sent a letter to the administration yesterday requesting additional information on the Sept. 11 attack on an American facility in Benghazi," Reid said. "These Republican colleagues said they would not allow a vote on Sen. Hagel's nomination to proceed unless the administration honored their request. The administration responded to that letter yesterday. I, along with several of my colleagues on both sides of the aisle, received a copy of the letter at 4 p.m. But now Republicans say this is not enough and are moving the goal posts at the last minute. This is no way to operate."

Meanwhile, McCain insisted he had been kept out of the loop.

"I have not received the letter," McCain told CNN Thursday morning. "They sent the letter to Sen. Levin. It was Sen Graham and I and Ayotte that asked for an answer. We haven't received an answer."

In the interview, he said the letter's delay was a chief reason he was holding up a vote on Hagel's nomination.

"I have to receive a letter, I have to receive a letter, see whether I receive a letter or not, and there are other questions that other senators have raised which are not answered as well," McCain told CNN.

Ultimately, Senate Democrats did not round up enough votes Thursday to break a filibuster on Hagel's nomination. A vote will occur after the Senate returns from its recess, when he is expected to be confirmed.

Relevant excerpts from both letters below: