As a non american i would like to know the real power of congress

So yeah basically, we are seeing a lot of congressmen/women coming forward on X posting about « we deserve to know » but what is really in their power ? I know the congress is a very powerful entity in the US democratic system but can we hope they can do something ? Is it a communication game they are playing ? What is their interests, and what can they really do to help the disclosure against agencies that are obviously very powerful too ?

Thanks