As for copyright status in the first instance, it depends on who is shooting the footage. If a private news station like CNN or CSPAN is filming the Congressional hearings, then those news companies will own the copyrights in the first instance. However, if U.S. Congress itself is filming its own sessions, it is probably public domain.
As of the time of this writing, U.S. Congress does not film its own regular sessions. However, occasionally, execute agencies may publicly broadcast their sessions. For example, early into Trump's administration, the FCC decided to revoke Obama's "net neutrality" executive order. That session was filmed and broadcast over a livestream on fcc.gov, thus making it public domain. Congress, however, does not normally film their own sessions (and in all fairness, they don't really have much need to, as private news companies tend to cover them just fine).
However, all is not lost. Every dark cloud as a silver lining. So here's the silver lining for your situation: If you're doing a political commentary channel, then as long as you provide actual COMMENTARY about the politics, it should be fair use anyway.
The important thing is to not skim on the commentary. Just remember: As far as courts are concerned in fair use cases, there is no such thin as "tranformative overload." There is no such thing as providing too much additional value. So be sure to go overboard with your opinions, criticisms, and discussions in order to maximize your chances of getting fair use protection.
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