Congress is sovereign so it can do as it pleases. Doesn’t mean others must cooperate, Congress has almost no tools to directly enforce its will.
If they actually pull out the ability to jail someone for contempt in Congress’ own brig, that will be leveraged to hell and back against them when they lose the House again in 2020.
Eric Holder was already found in contempt of Congress, so he can be arrested and held indefinitely from the day the new Congress is sworn in.
The Democrats seem to be desperately seeking a way to stop Trump from winning in 2020. They are not doing anything to help the American people either.