Is leadership in Congress an oxymoron?

There was an odd hubbub in Congress yesterday as the FBI executed a search warrant against William Jefferson, a congressman from Louisiana. Mr. Jefferson is accused of taking bribes. There seems to be some pretty strong evidence that he did what he is accused of based on a search of his house and video and audio tapes. Yet, the Speaker spoke out against concluding the investigation of this scumbag with the lame excuse that it might interfere with the immunity that members enjoy based on speech and debate. Is accepting a bribe in line with the intent of that section of the clause? Is it really a part of Mr. Jefferson's official duties to take bribes? If that is the best the GOP can put up maybe there is a good reason to change the leadership. One wonders what Hastert was thinking - or more on point whether he knows how to think.