He can't release everything IF, and it's a big if, they are actually going to prosecute the coup plotters, and those in the Obama Administration who used the full intelligence apparatus of the United States of America against a political opponent in the opposite party. Makes what Nixon did coving up a break-in look like shoplifting as opposed to armed robbery and murder.
The Democrats are freaking out, because if what they did is exposed and prosecuted it may be the end of them.