Again, the legal details of declassification are available HERE. The motive for the FBI and DOJ to refuse the “sources and methods” declassification request is outlined HERE.
The executive branch is in a squabble against itself due to malfeasance inside its law enforcement arm. It has been framing the President for crimes that Congress suspects he didn’t commit.
It’s the executive branch that’s “framing the President”; and the legislative branch trying to defend him.