Jubilant Democrats across America are declaring that their big election victories in Virginia and New Jersey - their first of the Trump era - mark the beginning of an anti-Trump surge that could reshape the balance of power in US Congress next year.
Senate Democratic leader Chuck Schumer says he can "smell a wave coming".
Not so fast, Republicans said. But they acknowledged that setbacks in Virginia, New Jersey and elsewhere on Tuesday created new urgency for Donald Trump's party to fulfil its list of campaign promises before voters head back to the polls for midterm elections in 2018.
They, along with Trump, have failed to demolish "Obamacare" and now are straining to approve a far-reaching tax overhaul, despite controlling the White House and both houses of Congress.
"If anything, this just puts more pressure on making sure we follow through," House Speaker Paul Ryan said at an event hosted by the Washington Examiner.
"I think it simply means we've got to deliver."
Whether the President's party delivers or not, there is clear cause for concern for a Republican Party that would lose its House majority if Democrats gained 24 seats next fall.
Tuesday's results left little doubt that Trump's dismal approval ratings can drag down Republican allies, particularly those serving in states he lost last November.
And even if his ratings show signs of improvement, history suggests that the first midterm elections for any new president often lead to major gains for the opposing party.
An early string of Republican retirement announcements in competitive districts across Florida, New Jersey and Arizona adds to the Republicans' challenge.
"We're taking our country back from Donald Trump one election at a time," Democratic National Committee chairman Tom Perez said on Wednesday.
"This is not just one night. It is a trend."
Senator Schumer added: "Our Republican friends better look out."
Trump declared the blame for Tuesday's losses was not his.
"Ed Gillespie worked hard but did not embrace me or what I stand for," the President tweeted as he toured Asia.
Actually, Gillespie, a mainstream Republican who lost the Virginia governor's race, had taken up Trump-like positions on such issues as Confederate monuments, NFL players' national anthem demonstrations and the dangers of Hispanic gangs.
Trump endorsed him but was not invited to campaign in the state in recent weeks. Republican National Committee chair Ronna Romney McDaniel had a different view from Trump's.
"I absolutely think any candidate should be embracing the president," she said, "and I think Ed did."
As for Tuesday's longer-term significance for the Democrats, both parties' leaders know that much can change in the year before voters decide the 2018 midterm elections. And Republicans enjoy a redistricting advantage that limits the number of truly competitive House races, thanks in large part to Republican routs during Barack Obama's eight years in office.
Also, Democrats wrestle with their own party strife, pitting the Bernie Sanders' wing against the more mainstream.
The liberal group Democracy for America had abandoned Virginia's gubernatorial candidate, Ralph Northam, over immigration policy, then celebrated his win days later.
"The plus of a tidal wave like this is it washes away the stains of all the campaigns," DFA executive director Charles Chamberlain said.
Republican Party leaders also expect their political outlook to improve dramatically once the Congress takes action on taxes or health care. Based on Tuesday's results, they need to act quickly.
Governors' races in Virginia and New Jersey - where Phil Murphy will replace Republican Chris Christie - were perhaps the most consequential, but Democrats also celebrated victories in Maine, where voters slapped the state's Republican governor, a Trump ally, by backing a measure to expand Medicaid coverage under Obama's health care law.
Manchester, New Hampshire, elected its first Democratic mayor in more than a decade. And Virginia voters sent a large and diverse group of new Democrats to the statehouse, including a transgender heavy metal singer, a member of Democratic Socialists of America and a former news anchor whose journalist girlfriend was fatally shot while on-air in 2015.
The results were particularly troubling for Republicans serving in suburban districts in states Trump lost last fall.
Senator Schumer singled out by name one of the most vulnerable House Republicans in the nation, Barbara Comstock, whose northern Virginia district lies just west of Washington.
Roughly two of three voters in the counties that primarily make up Comstock's district backed the Democrat in this week's governor's race. Sensing opportunity, more than a half dozen Democrats have already lined up to challenge her.
A spokesman for Comstock said Democrats had regularly underestimated the two-term congresswoman.
"Barbara has always over-performed and that won't change in 2018," political director Ken Nunnenkamp said.
Trump's team concedes the Republican Party's suburban challenges but predicts voters will bounce back once the Congress begins to enact his agenda. Embedded in that diagnosis, however, is a warning for Republican politicians that continued inaction could be disastrous.
Republican senator Thom Tillis of North Carolina acknowledged the urgency for his party to produce results.
"We've got to be RINOs," he said, "Republicans in Need of Outcomes."
AP writers Zeke Miller, Erica Werner and Juliet Linderman in Washington and Nicholas Riccardi in Denver contributed to this report