For a while everyone thought it would be enough to blame Dick Cheney.

President Obama assured the CIA that no one in the agency would be held accountable for the years of torture, abductions and killings, along with the mass surveillance of Americans, conducted under dubious legal authorisations.

America's intelligence community breathed a sigh of relief at what it took to be a commitment that if anyone was to be brought to book it would be the politicians who the agency enthusiastically served as it slipped the leash of legal restraint, particularly the former vice-president who fronted the Bush administration's war on terror. Most doubted that anyone would be held accountable.

But in recent days the ground has shifted dramatically, as a slew of revelations about the CIA's activities has left the agency facing its most hostile scrutiny since the 1970s, when congressional hearings revealed that it was pursuing its own, often illegal, agenda including numerous failed attempts to kill Fidel Castro.

Amid growing calls from within Congress for formal investigations and special prosecutors, former CIA officers say embittered agency officials believe they are caught up in a political war as the Democrats wield their newly acquired power to hit back at old foes in the Bush administration, particularly Cheney.

The CIA's critics say that it is coming under belated scrutiny over its submission to a highly political and possibly illegal agenda that its officials embraced with enthusiasm in the febrile atmosphere after the 9/11 attacks, when the Bush administration thought it could throw out the rule book by declaring the Geneva conventions out of date and redefining long established parameters for torture.

Even where questionable practices were declared legal by the administration, they remained of dubious morality such as the practice of kidnapping suspected terrorists and flying them half way around the world to be tortured and interrogated, known as rendition.

Some former CIA officers, including the former counter-terrorism chief of operations, Vincent Cannistraro, say the agency involved itself in suspect practices as it rode roughshod over long established restraints.

"There were things the agency was involved with after 9/11 which were basically over the edge because of 9/11. There were some very unsavoury things going on. Now they are a problem for the CIA," he said. "There is a lot of pressure on the CIA now and it's going to handicap future activities."

The CIA made two mistakes. The first was to think that it could keep it all hidden.

There is much that will never be made public, it was perhaps inevitable that something damaging would come out. As it happens, a slew of revelations have emerged with shocking speed.

In recent days, the agency has admitted hiding from Congress - probably illegally - a covert anti-terrorism programme. Numerous leaks have revealed it to be an operation to kill al-Qaida operatives, sometimes in friendly countries. The leaks have not been denied by the CIA or members of Congress since informed about the programme.

That revelation came days after five federal inspectors general released a report in to the role of the CIA and the National Security Agency in to warrantless wiretaps and other surveillance at the behest of the White House.

The CIA was just reeling from that blow when the attorney general, Eric Holder, said he wants a probe in to whether the agency was using waterboarding and other tortures even before the administration gave dubious legal opinions which cleared the way and swept aside years of precedent.

Few doubt that there will be more revelations to come, particularly if an increasingly agitated Congress decides to dig deeper.

Peter Bergen, an expert on intelligence at the New America Foundation, said that the CIA is not likely to be put through the wringer in quite the way it was in the 1970s when senator Frank Church's committee laid bare an array of illegal activities. But the agency will have to account for recent actions.

"The abuses by the CIA that Church revealed were worse than anything likely to come out of this. There were eight separate attempts to assassinate Castro. But the steady drip drip of revelations that's coming out now is very damaging to the CIA," he said. "The cumulative effect is a very large amount of dirty laundry will be aired and it will have an effect on the CIA, a very damaging effect."

Shortly after he assumed the presidency Obama reassured CIA officers that they would not be held to account for the abuses of the Bush years. Some took that to mean that the slate was wiped clean and that if there was to be any accounting at all it would be of a narrow group of political leaders.

Obama was keen not to lose the support of the security establishment, particularly as he faced down Republicans and some of his own party over the dismantling of the Guantanamo prison and the release of its inmates.

But Bergen said that the recent revelations have undercut Obama's assurances and encouraged Congress to wade in.

"All these things contribute to create the possibility to have a special prosecutor without being accused of a witch hunt," said Bergen.

There are many in the CIA who remain convinced that the agency is caught up in a political vendetta in part aimed at clearing the speaker of the house, Nancy Pelosi, of accusations she lied when she said the CIA hid waterboarding from her at intelligence briefings.

Cannistraro said the fact that there was a leak after the CIA director, Leon Panetta, recently admitted to the intelligence committee about the secret assassination programme has reinforced the perception that Congress is unreliable and the agency is caught in a political web.

"There's concern at the agency that they brought it to Congress's attention and it promptly leaked," he said.

But Cannistraro said that there is also a recognition within the CIA that the ground has shifted.

"The impulse for revealing this [secret programme] came from far below Panetta's office. It's part of the process to protect the hind quarters of the agency itself because there are things they recognise were over the edge," he said.

Cannistraro said that scrutiny of the CIA will require further examination of the politicians involved, and that it won't stop with the former vice-president.

"They keep specifying Cheney, but what Cheney did was endorsed by the president and Bush's office. This was not a one-man operation," he said.

The CIA's second, and perhaps greater mistake, was that all of the dark programmes appear to have been largely for nothing.

There is now ample evidence that interrogators learned most of what al-Qaida detainees had to tell before they were repeatedly water boarded.

Rendition, torture and Guantánamo are likely to have done more to have enhanced terrorism than curb it.

The inspector general of the justice department said of the secret surveillance programme that most of its leads "were determined not to have any connection to terrorism".

"There are plenty of people who view that the ends justifies the means," said Bergen. "The problem with Cheney is there were not ends. The waterboarding derived intelligence of no great value. I think it'll become clear these extreme measures were counterproductive and above all didn't find anything. That is going to be a very damning judgement for the CIA."