A good question.
Who told Karl about Valerie Plame? He ran the political side of the White House when he leaked the information--not the military/intelligence side. The answer to that question may lead straight to the Oval Office. And in a normal world, that would bring this corrupt and criminal presidency down.
Notice how I'm not holding my breath. The real journalists, with investigative assets, sources and time to do this job the way it should be done, won't do it. Too hard, too expensive, too much potential downside. Better to cover it as a "me-too" kind of story until it gets pushed down by the news cycle.
Despite being caught red-handed, Rove will not be indicted, and he'll keep his job. Bush can't function without him. Lying and criminal behavior aren't punished in Bushworld, because such behavior is endorsed as acceptable means to an end. Bush is a Management By Objective kind of guy. As long as you get him the war, the power and the paybacks that he wants, your methods are of no concern to him. Anyone who advises him that his objectives may not be the right ones for the country is removed. Ask Colin Powell.
The only real offense, the one that will get you in deep trouble, is disloyalty. Everyone who comes in contact with Bush knows that. Ask the wrong question, say the wrong thing, get branded as not-a-team-player, and your Washington career is over.
Karl is very loyal. Nearly all of the GOP members of Congress are very loyal. Porter Goss is very loyal, in spite of the wicked America-hating traitors that he supervises at the CIA. This will all blow over, and George and Karl will have a good laugh about it some day, after Jeb's inauguration. Just watch.