They can, however, be expelled from Congress by a 2/3 vote of the body
I did not know that! What are they waiting for!
It is up to the Democrats- who are in control of the chamber- to push it through.
The down side to them is that Minnesota is in play for 2020, and they might think that expelling this Omar broad will alienate voters in the Minneapolis area and cost them the state.
Even if they see this as a positive, the price they will have to pay to get the Republicans to go along with it might be higher than they want to pay as well. The Democrats best hope is to get Omar to quit voluntarily.