As I see it the conservatives are terrified what would happen if the Russian influence case proves there was any collusion.  Once the Republicans took a position, there was no collusion,  they committed themselves to live with the  voters reaction to the finding of any investigation.  Finding that there was collusion would be the biggest issue for the 2018 and 2020 elections that would end the existing majority in the House and Senate   Politics is a matter of perception.