The menacing thunder couldn’t get much louder for Democrats.

Few in the party had high hopes that their era of rule in Washington would last beyond the midterm elections next year. But the Republican resurgence on Tuesday in Virginia — a state that President Biden won by 10 percentage points last year — and surprising strength in solidly blue New Jersey offer a vivid warning of the storm clouds gathering as Democrats look warily to the horizon.

For five years, the party rode record-breaking turnouts to victory, fueled by voters with a passion for ousting a president they viewed as incompetent, divisive or worse. Tuesday’s results showed the limitations of such resistance politics when the object of resistance is out of power, the failure of Democrats to fulfill many of their biggest campaign promises, and the still-simmering rage over a pandemic that transformed schools into some of the country’s most divisive political battlegrounds.

In Virginia, the Democratic nominee for governor, Terry McAuliffe, was beaten with relative ease by Glenn Youngkin, a Republican private equity executive and political newcomer.

In New Jersey, Gov. Phil Murphy, a Democrat, faced a stunningly close race after being expected to coast to victory. In Minneapolis, voters rejected a ballot measure pushed by progressives that would have replaced the Police Department with a public safety department.

Perhaps most strikingly, the crushing setbacks for Democrats in heavily suburban Virginia and New Jersey hinted at a conservative-stoked backlash to the changing mores around race and identity championed by the party, as Republicans relentlessly sought to turn schools into the next front in the country’s culture wars.

For Democrats, the results on the nation’s single biggest day of voting until the midterms next year raised alarms that the wave of anti-Trump energy that carried them into power has curdled into apathy in a base that is tired of protesting and is largely back at brunch. Or, in what would be even more politically perilous, that the party’s motivation has been replaced by a sense of dissatisfaction with the state of a country that has, despite all of Mr. Biden’s campaign promises, not yet returned to a pre-Covid sense of normalcy.

In the coming days, Democratic anxieties and recriminations over the party’s loss in Virginia — the marquee race of the off-year elections — will echo from those suburban swing districts to Capitol Hill, as the midterm map extends into areas once considered safer for Democrats.

Even before the race was officially called for Mr. Youngkin, Democratic strategists were calling for their party to examine whether continuing to focus on Mr. Trump remained the best strategy, particularly after an election in which Mr. Biden promised his supporters that they would no longer have to worry about — or even think about — the round-the-clock drama of the previous administration.

“The Democrats need to take a serious look at how we chose to engage with the Trump narrative,” said Dan Sena, a Democratic strategist who helped the party win the House in 2018. “This was an election where the Democrats did not lean into their accomplishments either in Virginia or nationally. And as we look to 2022, we’re going to have to ask some hard questions about whether that’s the right strategy.”

Off-year elections have never been perfect predictors of future success. And even before the Virginia race tightened in late August, the national environment looked inauspicious for Democrats, who may lose seats in redistricting and face the historical trend of a president’s party losing seats during his first term in office.

But in a state where elections tend to be interwoven with national politics because of proximity to Washington, it’s hard to separate Mr. McAuliffe’s defeat from worsening views of the administration. In the week before Election Day, likely voters in Virginia disapproved of Mr. Biden’s job performance by 53 percent to 46 percent, according to a Washington Post-Schar School poll. Forty-four percent of voters in the state strongly disapproved of the president’s performance, compared with only 21 percent who strongly approved.

Even more worrisome for Democrats: Significant majorities now believe the country is headed in the wrong direction.

Republicans argue that Democrats and Mr. McAuliffe’s campaign failed to address what is behind that sense of decline: increased costs of groceries and gas caused by inflation; continued frustration with schools; supply chain challenges; and crime.

“When you look over the horizon for next year, the red wave is coming,” said Corry Bliss, a top Republican strategist working for a number of congressional candidates, who added that Democrats in Washington were not “fighting about things that normal people care about.”

As the country’s political pendulum appeared to swing back to the right, Republicans crowed that their party had hit upon a playbook for their candidates to replicate across the midterm races.

Democrats argue that history worked against Mr. McAuliffe. The candidate from the party not occupying the White House has won the Virginia governor’s mansion in 10 of the last 11 elections. The only exception: Mr. McAuliffe, who overcame that pattern to win his first term in 2013. Even then, Republicans won the midterms a year later and captured control of Congress.

In those 2014 races, many of the most vulnerable Democrats fled from President Barack Obama, hoping to save their seats by distancing themselves from his agenda. There’s little expectation that those dynamics will repeat over the next year, given the widespread recognition among congressional Democrats that the party’s fortunes are tied to the man at the top.

And yet self-preservation remains one of the most powerful forces in politics, leaving many strategists pessimistic that the party will unify around a central approach as Democrats in competitive midterm races grow increasingly nervous.

Moderate Democrats argued that the defeat was a sign that Congress must immediately pass the party’s infrastructure bill, regardless of what happens with the shrunken version of Mr. Biden’s legislative agenda. The left blamed the failure of the party to push a broader agenda, including overturning the filibuster to pass liberal priorities like bills protecting the right to vote. And political strategists fear that the party is failing to adequately communicate what Democrats have already done to help the Covid-ravaged country and why they haven’t delivered on issues important to their base.

“I’m worried, honestly,” said Adrianne Shropshire, the executive director of BlackPAC, a super PAC that aims to energize Black voters. She said voters of color had been disappointed by the inability of Democrats to pass laws on issues like voting rights and criminal justice. “People don’t want to be gaslighted about what’s not happening and why, by being told that everything is great.”

Yet as Mr. McAuliffe begged the White House and Speaker Nancy Pelosi to push for passage of the infrastructure bill, he took a much less aggressive approach to another issue: schools.

With their focus on “parental rights” — a catchall rallying cry capturing conservative outrage over mask mandates, vaccination requirements, transgender rights and how the history of racism is taught — Republicans found an issue that energized their voters, uniting the white grievance politics of the Trump base with broader anger over schooling during the pandemic.

Even though Mr. Youngkin offered little to address the endemic problems facing education that have worsened because of the coronavirus, schools became the central battleground of the campaign, rivaling the economy as the most significant issue for likely voters in the final week of the race, according to surveys.

By promising at nearly every campaign stop to ban critical race theory, an advanced academic concept not taught in Virginia schools, Mr. Youngkin resurrected Republican race-baiting tactics in a state that once served as the capital of the Confederacy.

Mr. McAuliffe dismissed those arguments and promised to pour more than $2 billion annually into Virginia schools. Some Democrats say that approach was insufficient given the conservative media’s daily amplification of spurious claims about classroom instruction on race as well as broader lingering frustrations among parents about schooling during the pandemic.

Instead of grappling with those thorny problems, Democrats cast back to their best motivator: Mr. Trump.

Mr. McAuliffe’s campaign maintained that even out of office, the former president remained Democrats’ most powerful weapon in a race widely expected to hinge on which party could best motivative its base. Mr. Youngkin, a fleece-vest-wearing businessman, became “Trump in khakis,” in Mr. McAuliffe’s phrasing, and his support for Trumpian issues like “election integrity” became the centerpiece of the Democratic pitch.

When Mr. Biden arrived in Virginia for a campaign rally a week before Election Day, he trained his fire heavily on Mr. Trump, barely mentioning his own agenda. The remarkable tableau of a president devoting his bully pulpit to the man he had defeated only served to underscore how little of an affirmative message Democrats were offering to voters.

“This has been a negative Trump-focused scare tactic campaign, and I think the top line is the declining salience of that,” said Tré Easton, a senior adviser for Battle Born Collective, a progressive advocacy group. “You can’t scare people into the polls. You have to give people something to vote for.”