Many Democrats are deeply, emotionally committed to resisting Trump. Sixty-six House Democrats voted to allow impeachment articles to move forward a year ago. Now, with the House in Democratic hands, and after another year of media-hyped Trump-Russia allegations, there’s no reason to believe Democrats would abandon the Russia issue regardless of what Mueller does.
In addition, some Democrats are warning that the public might not see all of Mueller’s report. Justice Department rules don’t require it, and attorney general nominee William Barr, in recent confirmation hearings, did not promise to release the whole thing.
So now there is talk about starting a new House Trump-Russia investigation that would essentially replicate what Mueller is doing now, but with the assurance that the proper (anti-Trump) result would be reached and that it could be used for impeachment purposes.