How does Peter Strzok impact Mueller's investigation?

Peter Strzok has been shown to have an incredible pro-Clinton/anti-Trump bias and made a comment to friends about having an “insurance” policy in case Trump was elected. He was a lead investigator on Robert Mueller’s team. Since he was integral to Robert Mueller’s investigation, in fact to all the allegations against Trump, does this cast a shadow on the validity of any findings Mueller might come up with? Another related thought is should the Clinton email scandal be reinvestigated since Strzok was also a lead investigator on that investigation?