This is a power they granted themselves. I don’t think you’ll find it in the constitution.
The power is valid. But as with everything it touches, Congress abuses and makes a joke of its powers. It is a failed institution.
It is better known as a Bill of Attainder.
Im not sure we can even consider it a power when it is so entirely inconsequential.
These Democrats are exercising their right to free speech like any other citizens - the only difference being an exaggerated sense of self-importance while doing it.