VA is blue now due to high populations of government workers, immigrants and government contractors in northern Virginia. Drastically cut government and the need for government workers and contractors declines.
Throw in the fact that Gillespie was a poor candidate.
He was boring and represented the GOPe Jeb Bush faction. The Republican base was not motivated to come out and vote in the same numbers as the 2016 election (Which was won by Hillary Clinton by less that 5000 votes).
Republican voters do get complacent sometimes on off years, while the rat agitators always vote (whether in person or by fraud)
It’s a welfare state now filled with gibmedats and other less than self-sufficient humans.
NC is not far from behind either.