The interruption was unplanned but Joe Biden immediately knew this was no ordinary heckler. “I agree!” he told a babbling baby as the audience laughed. “I agree completely. By the way, kids are allowed to do anything they want when I speak so don’t worry about it.”

It was a welcome note of light relief during a speech that could not be described as blockbuster television. Beside a blue sign that said “Building a Better America,” perched on a white boat at the New Hampshire Port Authority in Portsmouth, the US president was last week trying to gin up enthusiasm about infrastructure investment and supply chains.

Biden’s choice of state was telling: Democratic senator Maggie Hassan faces New Hampshire voters in November as she seeks a second term in elections that will decide the control of Congress. And not for the first time, there are fears the Democrats have a messaging problem.

The party does have a story to tell about the creation of 7.9 million jobs – more over his first 14 months in office than any president in history – along with progress against the coronavirus pandemic, the passage of a $1tn bipartisan infrastructure law, diverse judicial appointments and leading the Nato alliance against Russia’s Vladimir Putin.

But opinion polls suggest this could be overwhelmed by Republicans’ characteristically blunt and visceral campaign targeting 40-year high inflation, rising crime, immigration at the Mexico border and “culture wars” over abortion, transgender rights and how race is taught in schools.

“Hearts beats charts,” said John Zogby, an author and pollster. “Very simply, look at the Democrats who’ve won the presidency: Jimmy Carter, Bill Clinton, Barack Obama, Joe Biden. Contrast the obvious empathy and real-life stories with Michael Dukakis, Al Gore, John Kerry, Hillary Clinton.

“It’s the ability to tell a story that relates to all Americans. All of which is to suggest that Republicans will tell stories that matter and Democrats will show statistics.”

The stakes this time could hardly be higher: the Senate is currently split 50-50, while Democrats can afford to lose only three seats in the House of Representatives if they want to retain control. Given the headwinds typically faced by the president’s party in midterms, Republicans believe both chambers are within their grasp.

Such an outcome could turn Biden into a lame-duck president, able to do little more than issue executive orders and veto legislation, while empowering congressional Republicans to launch investigations into his son, Hunter Biden, and other foes while paving the way for the return of the former president, Donald Trump.

The polls look bleak for Democrats. Last month, NBC News found that 46% of registered voters prefer a Republican-controlled Congress while 44% want Democrats in charge – the first time Republicans have led in this survey since September 2014.

Inflation fears dominate, according to online focus groups run last week by Navigator Research with swing voters in Nevada, North Carolina and Wisconsin. They found that presenting economic facts “only modestly moves the needle” and pervasive inflation concerns outweigh job creation.

A North Carolina woman who took part said of the economy: “So you can tell me it’s doing great but if I’m struggling to buy groceries and gas and will be out of a job in two months, that to me is saying no, it’s not really doing that great.”

Biden has attempted to shift blame for rising fuel costs to “Putin’s price hike” but with limited success. His public approval rating stands at 43%, according to a Reuters/Ipsos poll, with disapproval of his job performance at 51%.

Democrats’ four most-endangered Senate incumbents – Hassan of New Hampshire, Mark Kelly of Arizona, Raphael Warnock of Georgia and Catherine Cortez Masto of Nevada – duly seem to be distancing themselves from the president, for example by visiting the southern border and criticising his plan to lift a pandemic-era restriction there known as Title 42.

Biden, touring the country and refocusing on domestic concerns after two months dominated by Ukraine, wants to convince voters that investing in roads and bridges is a major accomplishment after years of unfulfilled promises from his predecessor. But most of the benefits will not be felt for years and even the word “infrastructure” tends to land with a thud.

There are further worries that the Democratic base, including many voters of colour, will stay at home on election day, disenchanted by the party’s failure to get gun safety, police reform and voting rights legislation through Congress. Biden no longer uses the phrase “Build Back Better” and is struggling to salvage parts of that plan to address the climate crisis.

Henry Olsen, a senior fellow at the Ethics and Public Policy Center thinktank in Washington, said: “The difficulty that Democrats have is that a message that would energize the base is not one that resonates with the centre. The swing voter does not prioritize voting rights, climate change, big expansion of spending. They want much more pedestrian things and Democrats have not yet figured out how to have a narrative that combines both.”

Republicans have the luxury of opposition, Olsen added. “When you don’t have the power to be for anything, it’s easier to be against something and that’s what you’re going to see: Biden inflation, Biden weakness, Biden liberalism, Biden socialism.

“They will try to paint the Democratic party as a whole with its left wing but, by and large, they will attack Biden and the Democratic party as out of touch and producing bad results for the average American on the things they care most about: crime, immigration and the economy. This is one of, if not the most, favorable environment for an out party that I’ve seen in my lifetime.”

Indeed, Republicans are exuding confidence despite still being in thrall to a former president who incited a deadly insurrection and despite offering no policy agenda. Florida senator Rick Scott, the chairman of the national Republican senatorial committee, published his own 11-point plan that includes forcing poorer Americans who do not currently pay income tax to do so, but it was swiftly disowned by minority leader Mitch McConnell.

Instead, Republicansare filling the vacuum by assailing rising prices at the petrol pump and at the supermarket (“Bidenflation”), increasing crime rates in major cities and Biden’s reversal of Trump-era policies on immigration. US authorities arrested 210,000 migrants attempting to cross the southern border in March, the highest monthly total in two decades.

The party has also reverted to its playbook of social and cultural hot-button topics, railing against a caricature of “critical race theory” (CRT) in schools and pushing state legislation to restrict abortions and ban transgender children from sport. It casts itself as a champion of “parental rights” while portraying Democrats as “woke” socialists bent on controlling lives’ and “cancelling” dissent.

Addressing the conservative Heritage Foundation thinktank in Washington last month, Scott warned: “We survived the war of 1812, world war one, world war two, Korea, Vietnam and the cold war. But now, today, we face the greatest danger we have ever faced: the militant left wing in our country has become the enemy within.”

Come election season, Democrats are often accused of bringing a power-point presentation to a bar brawl: trying to explain policies in intellectual paragraphs while Republicans spin slogans ready-made for car bumper stickers. But this time some Democrats say they are ready to take the fight to their opponents.

Congressman Eric Swalwell of California has just launched the Remedy political action committee, which turns Scott’s message on its head by contending that American democracy is “under attack from within” and promising to “hold accountable those who choose party over country.”

Swalwell said: “At the end of the day, elections are about A or B. It’s about drawing a contrast and we can just make it as simple as chaos or competency. When it comes to transitions of power, do you want violence or voting? When it comes to the character of who runs the country, do you want indecency or integrity?”

“When [pro-Trump members of Congress] Matt Gaetz and Marjorie Taylor Greene proudly declare that they’re not the fringe, they’re the base of the party, we’re going to make sure every voter knows that. That’s what they’re going to get if they give Republicans the keys to the country.”

One dilemma for Democrats is how much time they should spend harking back to Trump, reminding voters of the existential threat that his party still poses to democracy, versus a positive forward-looking vision that encompasses bread-and-butter concerns.

Swalwell acknowledges that Democrats must identify with the pain that people are feeling from inflation while also offering solutions. He points to last month’s example of the House passing a bill to limit the cost of insulin to $35 a month (Americans currently pay around five to eight times more than Canadians). Some 193 Republicans opposed the bill while just 12 voted in favour.

Swalwell said: “We’re going to make them own walking away from solutions that would help people. Their plan for the economy is that 100 million people will pay more in taxes: that’s Rick Scott’s rescue plan that they’re running on. As people pay more already at the checkout stand, Rick Scott would have most Americans pay more in taxes.

“It’s going to be about choices and, if we have the resources to tell America what the choices are, we’re going to win. Right now I see the punditry betting against us but I don’t see our supporters betting against us because, when you look at Democratic versus Republican fundraising quarter after quarter, we’re beating them. There’s no fatigue in our base. They get it.”

The four embattled Senate Democrats – Cortez Masto, Hassan, Kelly and Warnock – raised more than their Republican opponents in the first quarter of this year, boosting hopes that supporters will remain energized. Trump’s determination to insert himself into dozens of races with risky endorsements, campaign rallies and his “big lie” of a stolen election could also galvanize Democrats and independents.

Michael Steele, the former chairman of the Republican national committee, predicts that Republicans will pick up 30 to 35 seats in the House but Democrats might just hold the Senate. He said: “The Republicans’ main message is going to be Democrats can’t run the country. ‘I give you the economy. I give you culture. I give you crime.’ And the Democrats’ message is, ‘Can we get back to you in a moment?’ That sums up the 2022 election.”

He added: “Republicans don’t have to run on anything substantive; all they have to do is say, ‘gee, look how screwed up these guys are.’ You’re going to see Republicans run a culture war-based strategy that drives the fear and loathing that White suburban families, particularly women, have over things that are not even relevant to their children’s lives, like CRT. And Democrats will be sitting there pissed off at all the wrong stuff.”

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