The principle is old, but still valid. In this case, the killing of an American ambassador in Benghazi. Even the BBC's US correspondent Mark Mardell thinks that this is going to be a problem for the Obama administration:
However you read the motives, the state department and apparently the White House did get the CIA to change its story.I agree with other commentators that Hilary Clinton is the vulnerable one here. There are three main political entities - Obama, Clinton, and the Republicans driving the enquiries. Since Obama is already on his second term, the Republicans gain little from attacking him. On the other hand, Obama (like any second term president) is thinking of his legacy. So he can make common cause with the Republicans to divert blame for this (deplorable) incident to Clinton. Everybody wins! except for Hilary Clinton's 2016 Presidential campaign, which has just suffered a major hole beneath the waterline.
This is now very serious, and I suspect heads will roll. The White House will be on the defensive for a while.
Incidentally, I'm not persuaded that a different attitude from the State Department would have made much difference to the eventual outcome. In hindsight, it looks marginal whether the relevant aviation and ground assets could realistically have deployed to the site of conflict in time to avoid the deaths of the ambassador and his staff. That isn't the point, however. The point is that State was faced with a prolonged attack on a US ambassador, had military assets on hand which could plausibly have made a difference (based on the information available at the time) and chose to do nothing as the personally safest option. This was a disgusting dereliction of duty which deserves to be severely punished. It won't be, of course, but the attempts to cover up what happened may end up sinking the career of people at the very top.