Wasn't that already the case, though? These guys have been claiming there's a "deep state" conspiracy to "get" Trump since before he was even elected. They didn't need Devin Nunes for that.
Conspiracies have more strength if people can constantly add more fuel to fire. You can argue that some segments of trumpland would have had the opinion no matter what but the Nunes memo has likely expanded the number of people willing to accept that premise which, in turn, reduces pressure on republican lawmakers to deal with Trump's law breaking.