Four weeks out from an election and the Democrats are stuck with him. This should help Tillis to some degree. It could make people less likely to vote for Cunningham while still not voting for Tillis, effectively dulling support for the former. I question how many people this will actually sway from Cunningham to Tillis. Probably not many but the main impact may be decreased support for Cunningham overall.
He need only change a few minds, his polling is only about 5 back prior to this.