Less than a year after taking control of the White House and Congress, Democrats were reeling on Wednesday from a shocking defeat in Virginia and a too-close-to-call governor’s race in New Jersey as Joe Biden’s popularity sinks and his domestic agenda hangs in the balance.

In Virginia, a state that had shifted sharply left over the past decade and that Biden won by 10 points in 2020, Republican Glenn Youngkin, a political newcomer, defeated Democrat Terry McAuliffe, the state’s former governor. And in New Jersey, the Democratic governor, Phil Murphy, was struggling to turn back a challenge from Republican Jack Ciattarelli, an unexpected turn of events in a state that is even more reliably Democratic.

“Together, we will change the trajectory of this commonwealth and, friends, we are going to start that transformation on day one. There is no time to waste,” Youngkin said, addressing jubilant supporters in the early hours of Wednesday.

Republicans’ resurgence after five years of stinging defeats during the Donald Trump era offers a stark warning for Democrats already wary of next year’s midterm elections. Their wins have echoes of 2009, when Republican victories in Virginia and New Jersey presaged their stunning takeover of the House in the 2010 midterms.

“In a cycle like this, no Democrat is safe,” said Tom Emmer, chairman of the National Republican Congressional Committee. On Wednesday, the group announced it was expanding its list of Democratic targets for the 2022 midterms following Youngkin’s victory.

The final weeks of the governor’s race in Virginia were dominated by education, as Youngkin, a 54-year-old former business executive, sought to harness parents’ frustration over school closures, mask mandates and anti-racism curriculum.

Exploiting the nation’s culture wars over race and education, Youngkin repeatedly promised to outlaw “critical race theory”, an academic concept about the effects of systemic racism that is not taught in Virginia schools but has nevertheless galvanized conservatives across the country.

McAuliffe, 64, worked relentlessly to tie his opponent to Trump in an attempt to revive the backlash to Trump that powered Democratic gains in recent years. But the effort was in vain.

Exit polls showed Biden was nearly as unpopular as Trump in Virginia, with Youngkin outperforming the former president in counties across the commonwealth. His success offered Republicans a strategy for how to mobilize Trump’s most ardent supporters while appealing to moderate voters in the suburbs who felt alienated by the former president.

Tuesday’s elections were the first major test of the national mood since Biden took office in January, and the results were deeply disappointing for the president and his party as they try to keep control of wafer-thin majorities in Congress.

Democrats were not well served by Biden’s sagging poll numbers, which have slumped to near-historic lows after months of infighting among Democrats over his nearly $3tn legislative agenda on Capitol Hill, a devastating evacuation from Afghanistan and the ever-present threat of the coronavirus.

“This election is a warning for all Democrats,” Guy Cecil, chair of the Democratic political group Priorities USA, said in a statement. “While DC Democrats spent weeks fighting each other, Republicans were focused on mobilizing their base and peeling away voters from the Biden coalition using deceptive, divisive tactics.”

It remains unclear whether the defeat in Virginia will spur Democratic lawmakers to action on a shrunken version of Biden’s agenda – or if it will cause them to retreat from the sweeping plans.

On Wednesday, the House speaker, Nancy Pelosi, signalled that Democrats were prepared to charge ahead as planned. She announced that the rules committee would hold a hearing on the $1.75tn domestic policy and climate mitigation bill, paving the way for a vote on the legislation and a companion $1tn infrastructure measure.

“Today is another momentous day in our historic effort to make the future better for the American people, for the children, to Build Back Better with women, to save the planet,” Pelosi wrote in a letter to Democrats on Wednesday.

Arriving at the Capitol on Wednesday morning, Pelosi brushed off any suggestion that McAuliffe’s loss changed the outlook for their agenda. “No, no,” she told reporters.

But in the wake of Tuesday’s elections, some Democrats expressed fresh doubt about the party’s resolve to enact both pieces of Biden’s agenda. Centrist lawmakers said the defeat was reason to swiftly pass the bipartisan infrastructure bill, regardless of what happens with the larger spending measure, amid concern that the effort would further alienate moderate and suburban voters who were critical to Biden’s victory in 2020 but shifted back toward Republicans in Virginia on Tuesday.

But progressives argued that abandoning their ambitious policy proposals would only spell further doom for their party, in desperate need of an economic message.

“The lesson going into 2022 is that Democrats need to use power to get big things done for working people and then run on those accomplishments. Period,” the Progressive Change Campaign Committee said in a statement.

“Democrats won’t win simply by branding one opponent after another as a Trump clone, and then hoping to squeak out a razor-thin win. When Democrats fail to run on big ideas or fulfill bold campaign promises, we depress our base while allowing Republicans to use culture wars to hide their real agenda.”

Democrats have only a five-vote margin in the House and are tied in the Senate, relying on the vice-president’s casting vote. Historically, the party in power in the White House almost always loses seats in Congress.

Elsewhere across the US, it was a night of historic firsts for Asian American candidates, a sign of the growing political strength of the AAPI community amid a rise in anti-Asian hate.

Michelle Wu became the first woman and person of color elected to be mayor of Boston in the city’s 200-year history. Wu, a progressive Democrat endorsed by her former Harvard law professor, the Massachusetts senator Elizabeth Warren, defeated fellow city councilor Annissa Essaibi George, who ran as a pragmatist with the backing of the city’s traditional power players.

In Cincinnati, Aftab Pureval, the son of immigrants from Tibet and India, defeated the former Democratic congressman David Mann. In Dearborn, Michigan, voters elected Abdullah Hammoud, a state lawmaker, as its first Arab American mayor.

In New York City, Democrat Eric Adams, a former NYPD police captain, was elected mayor of the nation’s largest city. He will be the second Black mayor in the city’s history.