The nation's top spy unexpectedly announced his resignation on Thursday, as Director of National Intelligence Dennis Blair is out after 16 months on the job, signaling unrest within the intelligence ranks of the Obama Administration.

"It is with deep regret that I informed the President today that I will step down as director of national intelligence," Blair wrote in a message to the intelligence community.

Blair's time in the job had been marked by two botched terrorist attacks, the Christmas Day airline bomb plot and the recent Times Square failed attack.

A member of the Senate Intelligence Committee told me that it was clear the White House wanted Blair out, as word leaked that replacement candidates have already been interviewed for the job.

Blair's last day will be May 28.

It was not immediately clear what brought about the move, but it was widely known that Blair had clashed with other intelligence leaders in the Obama Administration, a classic intelligence turf-war which never seems to end, no matter who is in charge.

Much of that conflict was reportedly between Blair and CIA Director Leon Panetta.

A former senior intelligence official in the Bush Administration says much of that turf war stems from the reforms made after 9/11, where the DNI job was created to better integrate the work of the various arms of the intelligence community.

He said most of the complaints heard in the press are directly from the CIA "who want to return to the good old days."

Republicans immediately denounced the ouster of Blair, accusing the White House of trying to use him as a fall guy for intelligence failures.

"It is unfortunate that the Obama Administration did not allow him to do his job and tried to make him the scapegoat for the Administration's intelligence failures," said Rep. Peter King (R-NY).

The move came two days after a Senate Intelligence Committee report was released, criticizing the overall intelligence community for committing many of the same errors in the time before the Nine Eleven attacks.

"The Committee concludes that the Intelligence Community failed to connect and appropriately analyze the information in its possession prior to December 25, 2009 that would have identified Abdulmutallab as a possible terrorist threat to the United States," the report stated.

No matter who gets selected to replace Blair, the hearings seem certain to take on a partisan edge - not only because it is an election year - but because terrorism and intelligence failures remain a political football in the post 9/11 era.

Another thing that deserves a review from Congress is the DNI job itself.  Created after 9/11, the job is nominally the "boss" of all the different spy agencies - but the DNI has been creating much of its own intelligence review structure as well.