First of all, to have Congress investigate intelligence failures is like asking the Madame to check her employees for VD. Lots of those failures are the direct responsibility of congressional investigations, hearings, breast-beatings and heavy-breathings that led to congressionally welcomed restrictions, parameters, and guidelines.
Let's just take a few, and then move on:
-- The Torricelli Rule, concocted in the Clinton years, according to which CIA was not permitted to have working relationships with people of dubious ethical standing. This utter absurdity (I mean, if CIA can't work with bad guys, why do we need a secret intelligence service? Even a foreign-service officer can talk to nice people) was swallowed whole by Clinton and Deutch;
-- The See No Evil rule, according to which the FBI was not even permitted to clip newspaper articles about openly violent anti-American organizations unless there was evidence they either had, or were planning to, commit a criminal act. This, and other insane restrictions, were swallowed whole by a series of feckless presidents and FBI directors;
-- The Executive Order banning assassinations, first enacted by President Ford and then expanded over the years to make it next to impossible for CIA to talk to anyone likely to kill anyone. In short, penetration of terrorist groups was off limits.
Any serious investigation of intelligence failures would include scrutiny of Congress's central role. But don't hold your breath.
Second, the really, really big intelligence failures are not investigated at all, because their causes are political. The three biggies are:
-- Saudi Arabia. How can it be that no one — not a diplomat, not a spook, not anyone, as far as I can tell — noticed that we were dealing with a fanatical regime that was financing a worldwide network of radical schools and mosques that indoctrinated young Muslims to wage jihad against us? Has clientitis gone so far that our people no longer have eyes to see or ears to hear? This is a truly monumental failure, and it requires serious analysis. But our paladins in Congress aren't looking that way;
-- Clinton, Sudan, and Osama bin Laden. Much is being made over the failure to get specific information about bin Laden's plans. Yet Clinton seems to have refused detailed information about bin Laden's years in Sudan. The Sudanese, trying to buy favor with us, offered to monitor bin Laden, report to us on his contacts, get us intelligence on bin Laden's conversations, or even turn him over to us. Clinton was not interested. Some sort of information was turned over to the Bush administration in the fall of 2001, but by then Osama had long since relocated to Afghanistan. Still, if Congress wants to catalogue missed opportunities, it would be worthwhile to look at that material in order to figure out how much damage the Clinton people did to us in this area.
-- Sunnis and Shiites: Until a few months ago, it was taken as gospel by the intelligence community that the branches of Islam were in such conflict it was virtually inconceivable that they could closely cooperate, even on terrorist actions against us. Events like the Iranian (Shiite) weapons ship "Karine A," discovered bringing arms and explosives to the (Sunni) PLO, have caused at least some of our smarter analysts to reconsider.
Let's hope they've learned their lesson and realize that Iran, Iraq, Syria, and Saudi Arabia are now working together against us. Otherwise our fighting men are likely to encounter some unpleasant surprises in the near future.