By Eric Bradner, CNN

(CNN) -- Democrats have won key races in Virginia and New Jersey, CNN projects, their first major wins during the tenure of President Donald Trump and a boost heading into the 2018 midterms, when control of US House and Senate will be up for grabs.

The blue wave along the East Coast saw Ralph Northam winning the governor's race in Virginia and Phil Murphy victorious in New Jersey. Democrats are also on pace to capture control of the Virginia General Assembly, and several liberals, including New York City Mayor Bill de Blasio won their mayoral elections.

Virginia's gubernatorial contest was the first major test of Democrats' ability to rebound after Trump's victory. The fundamentals of the state were in their favor: Under Democratic Gov. Terry McAuliffe, unemployment is lower than the national average, and voters have generally told pollsters that they see the commonwealth as on the right track while the nation is on the wrong track.

Northam's victory over GOP lobbyist and former George W. Bush aide Ed Gillespie -- clinched much earlier than nervous Democrats had expected -- left party leaders jubilant about their chances in the 2018 midterm elections, particularly in heavily suburban, Republican-held House districts that look much like the northern Virginia suburbs.

Gillespie distanced himself from Trump personally, but embraced much of the President's agenda, including a focus on illegal immigration and sanctuary cities. Gillespie also echoed Trump's calls to keep Confederate monuments in place and invoked NFL players kneeling during the national anthem.

But Trump immediately disavowed the GOP candidate Tuesday night even as votes were still being counted.

"Ed Gillespie worked hard but did not embrace me or what I stand for. Don't forget, Republicans won 4 out of 4 House seats, and with the economy doing record numbers, we will continue to win, even bigger than before!" Trump tweeted.

Democrats also made significant down-ballot gains in Virginia. Justin Fairfax won the lieutenant governor's against Republican Jill Holtzman Vogel, a state senator known for her sponsorship of a 2012 bill that would have required women seeking abortions to undergo vaginal ultrasounds. Social issues were prominent in another statewide race, where Democratic attorney general Mark Herring defeated Republican challenger John Adams, who has hit Herring for his refusal to defend Virginia's same-sex marriage ban in court.

And Chris Hurst, whose girlfriend Alison Parker was the Virginia TV reporter killed on live television in 2015, won a seat in the Virginia House of Delegates.

Around the country

Murphy's Garden State win will return the state to Democratic control after eight years under the leadership Republican Gov. Chris Christie.

Murphy defeated Lt. Gov. Kim Guadagno in a state where Christie's unpopularity -- with approval ratings in the teens, making him the least-liked governor in the country -- proved too much to overcome.

Elsewhere in the country, New York City, Atlanta and other cities are electing mayors. And in Utah, CNN projects voters picked Republican John Curtis to be a replacement for the retired former Rep. Jason Chaffetz, also a Republican.

In New York City, de Blasio -- who campaigned with Vermont Sen. Bernie Sanders and has fashioned himself as a leading progressive voice -- easily won a second term.

Across the country in Washington, a state senate match-up will decide whether Democrats take control of the chamber -- and therefore land the "trifecta" of control of both chambers of the state legislature and the governor's office.

Gillespie, Northam appealed to base voters

Gillespie leaned hard into the cultural battle in the race's final days.

His campaign's closing message was that Democrats had gone too far and portrayed all Republicans as racists -- pointing to a Latino Victory Fund ad that showed four minority children being chased through the streets by a white man driving a pick-up truck with a Confederate flag and a Gillespie bumper sticker. The group spent just $30,000 to air the ad and pulled it almost immediately, but Gillespie's campaign still seized on it.

Despite the ad strategy designed to turn out Trump voters, Gillespie and Trump never campaigned together, despite Trump spending 15 days at his Virginia golf course between Gillespie's primary win and the general election. Trump recorded a robocall on Gillespie's behalf that went to some voters Monday night and Tuesday, and tweeted urging voters to back Gillespie.

Gillespie had mimicked Trump's tactics -- attacking Northam over sanctuary cities while saying he would not remove Confederate Civil War monuments. A Gillespie mailer also referenced the controversy over protests by NFL players. "You'd never take a knee ... so take a stand on Election Day," the mailer reads.

But he has kept personal distance from Trump: The two didn't campaign together at all, despite Trump visiting his own golf course in Virginia 15 times after Gillespie won the Republican nomination.

Republicans nationally were closely watching to see if Gillespie's approach works or whether he got too close to Trump for suburban voters' comfort, or strayed too far away from the President to win over his rural, white base.

Northam, meanwhile, has struggled to motivate the black voters who make up the Democratic base. Former President Barack Obama urged Democrats not to get "complacent" in non-presidential elections during an October rally with Northam in Richmond.

Preliminary exit polls found that Gillespie's focus on keeping Confederate monuments in place could be popular with Virginia voters -- particularly Republicans and independents. Ninety-five percent of Republicans said the monuments should remain in place, and nearly eight in 10 independents agreed. Meanwhile, about seven in 10 Democrats said the statues should be removed.

Helping Northam, though, could be Trump's 43% approval rating among those who voted, according to the preliminary exit polls. Fifty-five percent of Virginia voters said they disapprove of how Trump is handling his job.

The Virginia race carries national importance as a gauge of how voters are reacting to Trump a year into his presidency -- and also because the state is a proving ground for both parties' approaches in the 2018 midterm elections, when Democrats hope to take control of the House and Republicans seek to expand their 52-48 Senate majority.

The election takes place with Trump overseas on a 13-day Asia trip. The President had thrown his political capital heavily behind Sen. Luther Strange in an Alabama Republican Senate primary in September -- but Strange lost to former judge Roy Moore, and Trump has been much less involved in subsequent races, although he continues to tweet to help Gillespie.