Republicans awoke Wednesday to a series of aftershocks following Democratic victories across Virginia and in other local elections that far exceeded either side’s expectations.

That performance, particularly in key suburban battlegrounds across the nation, validates a strategy that Democrats on Capitol Hill had embraced earlier this year — trying to win the majority by riding a wave of liberal resentment toward President Trump while also promising rational governance to centrist swing voters.

The resounding victory by Democrat Ralph Northam in the Virginia governor's race tells only part of the story of Tuesday's "old-fashioned thumping," as former Virginia congressman Tom Davis called it. Beneath the top-of-the-ticket races, in many fundamental places, the ground shifted against Republicans in ways that have properly struck fear in the hearts of GOP consultants.

Of eight Republican-held districts in the Virginia House of Delegates that touched at least part of the congressional district of Rep. Barbara Comstock (R), Democrats won at least six.

Comstock is considered one of the 10 most vulnerable Republicans in next year’s midterm elections.

How Northam gained in a more polarized Virginia

In the suburbs west of Philadelphia, Democrats romped. They won two countywide seats on the Delaware County Council for the first time ever and swept three other countywide offices in Pennsylvania's third-largest suburb. Democrats won first-ever victories in neighboring Chester County, as well.

The Republicans there tried to run as common-sense politicians who support low taxes, a message similar to what U.S. Reps. Patrick Meehan (R) and Ryan Costello (R) expect to run on next year in districts that include those onetime GOP strongholds in the suburbs. Democrats there, in contrast, ran against Trump and what they described as a local GOP machine governed by cronyism.

Voters wanted to "make a statement that Democrats are going to vote in the Trump era," David Landau, chairman of the county Democrats, told the Philadelphia Inquirer. "We're not going to go to sleep."

All told, Republicans can afford to lose only 23 seats in the House next year to retain the majority, but Democrats already have their eyes on dozens of suburban GOP seats that are competitive in presidential or other statewide races. It just so happens that 23 Republicans, like Comstock, sit in seats where Hillary Clinton defeated Trump last year, in addition to 13 that previously backed Barack Obama in his presidential races.

The Republicans were dejected seeing the results — left to question how much of a down-ballot effect Trump’s unpopular presidency will have on them next year and unsure about what they can do to appeal to voters.

House Republicans are already reeling from retirements by battle-tested incumbents in seats that could flip to the Democrats next year. Just Tuesday, before the election results came in, Rep. Frank A. LoBiondo (R-N.J.) announced that he would not run for his seat next year. Rep. Martha McSally (R-Ariz.) is leaning toward an up-or-out campaign for the Senate rather than fighting every two years to win her House seat.

Northam supporters erupt in joy as his victory is announced Tuesday in Fairfax. (Michael Robinson Chavez/The Washington Post)

Democrats know this feeling. Back in 2009, They tried to play down the Republican rout in the Old Dominion’s elections. Within a few weeks, several senior House Democrats announced they were retiring, and those seats flipped to Republican control for the first time in decades — part of a GOP wave that led to a 63-seat pickup and the majority.

Surveying Tuesday’s landscape, one senior GOP strategist summed it up this way: “Middle-class tax cut or else.”

The suggestion is that if Republicans can unite around a tax-cut deal in the House and get that signed into law, they will have a real achievement to sell to voters back home.

But that’s a long way from the emerging proposals in the House Ways and Means Committee and the Senate Finance Committee, which appear to be headed in different directions on key principles.

Senate Republicans, for instance, seem to favor a complete elimination of the deduction for state and local taxes on federal returns. In the House, that proposal is a potential death sentence for the more than two dozen Republicans from California, New Jersey and New York, a move that would be construed as a tax hike on their middle-class constituents in those wealthy, high-tax states.

Republicans even have reason to fear in districts that swung to Trump, such as LoBiondo’s in southern New Jersey. The 23-year veteran, having already opposed the GOP proposal to repeal the Affordable Care Act, voted against the budget outline that set the framework for the tax debate, over concerns about local tax deductions.

Even if they can sell the tax plan as benefiting most voters, Republicans have to look at Tuesday’s results and worry whether their playbook on taxes might come across as stale in this polarizing environment.

In the Virginia governor’s race, Republican Ed Gillespie spent the final week of the campaign blanketing the suburbs outside Washington with ads that promoted a traditional GOP view of lower taxes and job growth. That came after weeks of negative ads warning that Northam would support “sanctuary cities” that would lead to gang violence by undocumented immigrants.

Neither of those messages connected, particularly in Northern Virginia.

Gillespie lost Comstock’s 10th Congressional District by a double-digit margin. He more narrowly lost the 2nd Congressional District, in the southeast corner of the state — where Rep. Scott Taylor, a freshman Republican, was already facing a potentially tough race next year. Now Taylor is a bigger target. A year ago, Democrats basically forgot about this district and gave Taylor a virtual pass in the general election.

Northam had been mocked by liberal activists at the national level who thought his lack of emotional energy felt out of step with the times, leading to deep criticism of an ad in which the lieutenant governor briefly said he would work with Trump on issues that helped Virginians but overlooking the part of the ad that excoriated Trump.

In his victory speech, Northam delivered that same double-barreled message, something that more Democrats are likely to copy next year. He blasted Trump’s “hatred and bigotry” yet promised nonpartisan governance.

“We will put the people of Virginia before politics, before party, before ideology,” he said.

Read more from Paul Kane's archive, follow him on Twitter or subscribe to his updates on Facebook.