Midterm elections proved that Republicans have only a tenuous hold over the coalition that propelled Trump to the White House in 2016

Kyrsten Sinema became the first Democrat to win an Arizona Senate seat in 30 years. Photograph: Alexander Drago/Reuters

As the returns poured in on the night of last week’s midterm elections, a narrative swiftly began to take shape: although Democrats succeeded in retaking the House of Representatives from Republican control, the vaunted “blue wave” had failed to materialize.

But just over a week later, the assessment has evolved just as rapidly amid a series of gains by Democrats in contests that on election night were too close to call. Democrats have now picked up 34 seats in the House – a tally that may inch closer to 40 with a number of results still outstanding.

On Tuesday, the party was given another reason to rejoice when Kyrsten Sinema became the first Democrat to win an Arizona Senate seat in 30 years. Sinema’s hard-fought victory over her Republican opponent, Martha McSally, not only flipped a reliably red seat blue, but also countered the notion that Democrats had taken a beating in the Senate.

The revised outlook has reinforced the Democratic party’s momentum in the current political climate, while also exposing the Republican party’s vulnerabilities with Donald Trump at its helm.

The president sought to take a victory lap in the immediate aftermath of the 2018 midterms, insisting Republicans had exceeded expectations. And in characteristic Trumpian fashion, he added that those Republicans who did lose their seats were defeated over their refusal to embrace him.

Those that worked with me in this incredible Midterm Election, embracing certain policies and principles, did very well. Those that did not, say goodbye! Yesterday was such a very Big Win, and all under the pressure of a Nasty and Hostile Media! — Donald J. Trump (@realDonaldTrump) November 7, 2018

Trump’s claim was dubious then and even more questionable now, in the face of steady Democratic pickups in the week since the midterms. Contrary to the president’s efforts to downplay their outcome, the elections proved that Republicans have only a tenuous hold over the coalition that propelled Trump to the White House in 2016.

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“I think Republicans would be foolish to just think that this is simply a conventional midterm,” said Rory Cooper, a GOP strategist who served as a top aide to the former House majority leader Eric Cantor.

“You have an economy that’s roaring and unemployment that’s historically low … and so you have to look for other indicators for why you’d lose that many seats.”

Democrats needed to flip 24 seats in order to win back the House for the first time in just under a decade. The Senate map was less favorable to the party, with Democrats defending 26 seats – including many in states carried by Trump two years ago.

Although election night saw Democrats triumph in the House, their victory was somewhat overshadowed by the loss of a handful of candidates whose challenges in conservative strongholds had garnered national attention.

The Democratic congressman Beto O’Rourke, whose campaign inspired millions in deep red Texas, came within three points of toppling Senator Ted Cruz. In Kentucky’s sixth congressional district, former fighter pilot Amy McGrath ran a similarly upstart campaign, powered by the grassroots, but in the end her Republican opponent prevailed.

Until recently, it had been unthinkable that Democrats would mount credible challenges in such areas – which in part meant a disproportionate amount of coverage on the high-profile races where the party was ultimately unsuccessful.

A similar dynamic played out in two closely watched governor’s races, where two black candidates had hoped to make history.

In Florida, Andrew Gillum lost to Republican Ron DeSantis by a margin so narrow that state law forced an automatic recount. Although the results did not change the outcome of the race, progressives saw signs of hope in a state that has not elected a Democratic governor in 24 years.

Stacey Abrams, who had been vying to become the first black female governor in US history, conceded defeat in Georgia on Friday to her Republican opponent Brian Kemp. She nonetheless came remarkably close to forcing a runoff, with Kemp having won just a slim majority of the vote.

Democrats took some solace in their newfound competitiveness in the south and south-west and the prospects of transforming what had long been conservative terrain into potential battleground states.

The disappointing results in Florida and Georgia notwithstanding, Democrats otherwise saw more success at the state level than in any recent election cycle.

They flipped seven gubernatorial seats and six legislatures, enabling the party to enact progressive agendas statewide and exert influence over the redistricting process – to carve out future congressional maps – that is due to take place in 2020.

Democrats also made several unexpected pickups in the days that followed the midterms, which earned less focus given the delay in the results being declared.

They include Lucy McBath, an advocate of stricter gun laws whose son, Jordan Davis, was fatally shot in 2012 by a white man in a dispute over “loud music”. McBath defeated Republican Karen Handel in a Georgia congressional district once held by the former House speaker Newt Gingrich.

In New Jersey, Andy Kim, a former adviser to Barack Obama, ousted Tom MacArthur, a Republican congressman who had made himself the face of the party’s efforts to repeal and replace the Affordable Care Act last year. MacArthur’s loss, officially declared on Wednesday, left the New Jersey congressional delegation with only one remaining Republican.

Democrats also converted three House seats in California, defeating incumbent Republicans Jeff Denham, Steve Knight and Dana Rohrabacher.

“This was a great night for Democrats no matter what you want to call it. I’m more than willing to call it a blue wave,” said Jim Manley, who served as an aide to the former Senate majority leader Harry Reid and the late Senator Ted Kennedy.

Manley expressed frustration with the pundits who claimed on election night that Democrats had underperformed.

“The mere sense that we were going to pick up the House was a huge deal,” he said. “The whole goal, the whole crux of the last two years, was reclaiming the House.”

What was at first billed as a Republican rout in the Senate also looks far less certain one week later.

Although three vulnerable Democratic senators – Claire McCaskill in Missouri, Heidi Heitkamp in North Dakota and Joe Donnelly in Indiana – lost their re-election bids last Tuesday, the party held onto seats in Montana, West Virginia and Ohio, also states won by Trump in 2016.

In addition to Arizona, Democrats also moved Nevada to their column; and in Florida, the Senate race called in Republican Rick Scott’s favor on election night has since gone to a recount, giving Democrats a glimmer of hope that the incumbent senator, Bill Nelson, might still have a chance.

According to exit polls, healthcare was a top priority for voters as they cast their ballots. Democrats had fervently campaigned on protecting the coverage for pre-existing conditions afforded under Obama’s healthcare law.

Republicans, led by Trump, zeroed in on immigration in the closing weeks of the campaign. While stumping for Republicans across the country, the president repeatedly stoked fears over a caravan of migrants headed toward the US-Mexico border from Central America. (Trump has not mentioned the caravan since the midterms.)

The strategy was unmistakably centered on boosting turnout within the Republican base, but did little to draw support from independents, who swung toward Democrats. It also appeared to turn off suburban women, who increasingly disapprove of the president and proved decisive in the Democratic party’s success.

Cooper said the midterms revealed that Trump’s stunning victory two years ago “did not fix what’s ailing the Republican party”.

“The more you win in the short term, the more you can put off fixing long-term structural issues, like the age, race and gender of the typical Republican voter,” he said. “There was no effort to appeal to anyone outside of the normal base.”

“That is a huge blindspot for Republicans, if they continue to assume they can just win on turnout.”