In a conference call with reporters, Mr. Garcetti cited turnout increases of 76 percent in three Virginia congressional districts that include parts of Norfolk and the suburbs of Washington and Richmond.
Over all, 1.3 million voters in Virginia went to the polls on Tuesday, surpassing the votes cast in 2016 by nearly 70 percent and, even more stunningly, breaking a previous Democratic record of 986,000 votes set in 2008, when Barack Obama was on the ballot.
Democratic turnout on Tuesday was up broadly compared with 2016 — with Texas up 49 percent, Tennessee up 38 percent, and Vermont and North Carolina both increasing by 16 percent. Several states that had switched from caucuses to primaries this year — Colorado, Maine, Minnesota and Utah — also saw heavy increases in participation.
Nowhere was the Democratic boom more pronounced than in the tony Northern Virginia suburbs of Washington. Here, among the million-dollar homes populated by lobbyists, corporate lawyers and employees of government contractors, Mr. Biden ran up huge margins over Mr. Sanders and the rest of the Democratic field while turnout in some areas nearly doubled from the party’s 2016 primary.
The region, with its high population of educated professionals, was believed to be a good area for Ms. Warren and Pete Buttigieg, the former mayor of South Bend, Ind., before he ended his campaign on Sunday night.
Dan Helmer, who in November ousted the last remaining Fairfax County Republican in the Virginia General Assembly, said the rush of new voters helped catapult him into office. His victory, completing the Democratic sweep of the Washington suburbs, came after Mr. Trump alienated many of the federal workers and contractors.
“He has converted huge numbers of federal civil servants to Democrats,” said Mr. Helmer, who switched his support from Mr. Buttigieg to Mr. Biden on Monday. “It’s a pocketbook issue for Northern Virginia. Trump has just shook the earth in a way that it’s going to take years for Republicans to recover.”