He must resign. Ellison should be appointed.
By all means, appoint Ellison. That would certainly improve the GOP's chances of taking the seat. Whether he resigns or not, ambitious politicians in MN should be getting ready for a shot at the Senate soon enough. He won't run for reelection.
If these scandals keep breaking (supposedly there was a fund that paid out thousands if not millions in hush money to victims of Congressmen from both parties), we may finally get some turnover, at the cost of what little respect people still have for Congress. A Moore election won't help, but a defeat for him could also lead to an epidemic of allegations being saved until it's just a little too late to change the candidate on the ballot. Just when people thought politics could get no uglier.