In 2000 VA had two R senators, a R governor and Rs dominated both houses. In 20 years that has flipped. Yes Nova has lot of people and a lot of Democrats. But demographics cannot explain all of this. Something else is gong on.
Population Va increase 1 million over that time period. Some are children. Some are Republicans but at least ( I would guess ) 500,000 are Democrats. Lets say 40% actually vote. 200,000 new Democrats voters are NOT going to cause this flip.
Went from 7 million to 8,.6 million. Lots of turnout in that crowd. We had almost 80% in my Trump county but Fairfax had close to that. Assume new voters are more Dem than Rep. Current Fairfax breakdown was 70 to 28. Used to be close to 50/50 although probably already somewhat Dem in 2000.
Bottom line: 200k new Dems in Fairfax county alone.