Mamdani urged the city to "breathe this moment in."
Democrats triumphed in high-profile races that unfolded across the country on Tuesday, including New York City's mayoral election and governor's races in New Jersey and Virginia.
In California, voters also chose to redraw their state's congressional map in a move that could net Democrats five House seats.
The elections help provide a picture of how Americans feel about President Donald Trump's first nine months in office. Following a wave of Republican losses, Trump tried to blame the election results on his not being on the ballot and the prolonged government shutdown.
Affordability is the key theme in all of tonight's major races. And it’s clear why -- the typical American household is spending $208 extra per month right now on the same goods and services compared to this time last year because of inflation, according to Moody’s Analytics.
Households are spending $1,043 per month more now compared to the start of 2021 coming out of the pandemic.
-ABC News' Elizabeth Schulze
President Donald Trump claimed on social media that, according to pollsters, him not being on the ballot and the shutdown were "two reasons that Republicans lost elections tonight."
Trump did not name the specific pollsters in his post.
As of 10:10 p.m., with 95% of the expected vote reporting, Democrat Jay Jones is projected to win the Virginia’s attorney general race against Republican Jason Miyares by 5 points: 52%-47%.
Jones' campaign for attorney general was embattled in its final days, as Jones faced calls from Republicans to drop out of the race due to his recent texting scandal in which he was revealed to have called for violence against a Republican lawmaker. Jones apologized for the texts and said he will be "accountable for my mistakes."
-ABC News' Halle Troadec
ABC News projects Democrat Jay Jones will win the Virginia attorney general race against Republican incumbent Jason Miyares, based on an analysis of the vote.
