The chairs of the House and Senate Intelligence committees are cleared for everything ex officio, correct? Do they have the authority to declassify anything? Can they blab classified information to the press? Do they have to be vetted by the FBI? What about other members of Congress? What sort of access do they have to classified information? The President and Vice President are also cleared for everything, aren’t they? Can they classify and declassify information at will? I know they can’t classify things to conceal illegal activity, etc., but what about classifiable information?
No. The National Security Act requires that the President keep Congress “fully and timely informed” of intelligence activities. There are other activities – such as war plans – which Congress may not be privy to. In fact, Senator Bob Kerrey, then a member of the Intelligence Committee, led a quixotic campaign in the 1990s to force the disclosure of the SIOP, the nuclear war plans against the USSR/Russia, to the intelligence committees. He did not succeed.
Briefly, there’s a complex process that involves votes in the intelligence committees and the respective houses of Congress. They can’t up and decide to declassify anything.
Members of Congress get access to classified information by virtue of their election, not a security clearance, but the Senate and the House may impose restrictions, like the House required members to sign a non-disclosure statement.
The Executive Branch controls classification of information. There’s an Executive Order that establishes what may be classified, by whom, and at what level. Link.