U.S. Rep. Susan Wild was thrilled when President Joe Biden visited her Lehigh Valley district Wednesday. Jogging out between twin Mack trucks, an ebullient Biden promoted plans to aid manufacturing and, more broadly, middle-class workers.

Wild, a Pennsylvania Democrat facing one of the toughest reelection campaigns in the country, got more encouraging news during the visit, when senators reached a breakthrough on a bipartisan infrastructure bill, a major step toward another of Biden’s signature economic promises. And the next day, new data showed the U.S. economy had grown at a 6.5% annual rate last quarter, returning to pre-pandemic size faster than many expected.

“Notwithstanding what is often great dysfunction in Washington and great division, we have nonetheless managed to get a helluva lot done,” Wild said, pointing to increased child tax credits, aid to restaurants, and the potential infrastructure deal as a few examples.

But even as Democrats advance another piece of their agenda, warning signs are beginning to flash for Biden and his allies.

Republicans hoping to flip swing districts such as Wild’s and take control of Congress are pointing to rising inflation; spikes in murders, including in Philadelphia; and a continued influx of migrants at the Southern border. They’re criticizing how schools teach about racism in U.S. history and emphasizing business’ struggles to find workers.

Meanwhile the coronavirus’ delta variant has created new uncertainty around the economic recovery, prospects for school reopenings, and the hope for a return to normalcy. Although the economy is growing fast, the most recent quarterly number fell below economists’ projections.

Republicans have struggled to vilify Biden personally, but in their wide-ranging criticisms they see a menu of issues they hope can put them back in charge of Congress and stop the president in his tracks.

“The only thing made in America under the leadership of Joe Biden is a tanked economy with skyrocketing gas prices, skyrocketing crime, skyrocketing inflation, and a crisis at our Southern border,” Sean Parnell, a Republican Senate candidate in Pennsylvania, said in a statement about Biden’s visit, capturing the GOP medley.

Democrats argue that Republicans are flailing in the face of popular plans helping workers, parents, and communities.

“Republicans have just been throwing things on the wall and seeing what might stick, and nothing has stuck so far,” said Jessica Floyd, president of American Bridge, one of Democrats’ largest national super PACs.

Both parties may soon get a glimpse of whose message is resonating. Congress’ August recess, when lawmakers take a break from Washington and tour their districts, often provides an early gauge of the electorate — and hints of any simmering anger.

Democrats face a high-wire act. They hold the slimmest of majorities in Congress, and the party in power almost always loses ground in midterm elections.

Strategists in both parties say it’s too early to know what issues will dominate when people vote in November 2022. But with the $1 trillion bipartisan infrastructure bill gaining steam and Democrats also pressing ahead with a $3.5 trillion package for health care, child care, family leave, and other social programs, the economy appears to be the most immediate battleground.

“Inflation is a pocketbook issue and it’s going to impact everybody,” said Joe Gierut, a spokesperson for America Rising, a Republican opposition-research firm.

Consumer price increases hit a 13-year high in June, and 59% of voters blamed Biden’s policies, according to a July survey from Morning Consult. Nationally, 54% of adults think the economy isn’t doing well, according to a separate poll released last week by the Associated Press and NORC Center for Public Affairs Research, with responses split sharply along party lines.

Still, in that survey a small majority, 52%, approved of how Biden was handling the issue, and 59% approved of his performance overall. And the poll showed widespread support, including among Republicans, for the key elements of the infrastructure plan: billions for roads, bridges, water pipes, and broadband internet.

The economic debate will likely play out at full volume in Pennsylvania and New Jersey. At least a half-dozen congressional races, and possibly more, could prove competitive in the two states, giving them a significant role in the fight for the House, and Pennsylvania’s U.S. Senate battle is one of a handful that will determine control of that chamber.

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To Republicans, and some economists, the money Democrats tout from Biden’s $2 trillion American Rescue Plan, enacted in March, is fueling inflation, and new spending will only make it worse. The relief package included $1,400 stimulus checks, child tax credits of up to $3,600 for the vast majority of parents, and enhanced unemployment aid. Every congressional Republican opposed it.

“You can say you’re not raising taxes on middle-class families, but if the price of eggs, gas, and milk go up, they’re the ones that are going to be impacted more,” said Conor McGuinness, campaign manager for Jeff Bartos, a Republican Senate candidate from Montgomery County.

As Bartos toured the state in July, McGuinness said, he regularly heard worries about inflation and labor shortages, which Republicans blame on aid they say has discouraged work. In Allentown, not far from Biden’s visit, Bartos tweeted a photo of a business’ sign that read “Closed. Sorry short staff.”

Some labor advocates say it’s a good thing workers now have support and options. “They always said, it seemed, ‘Let the market decide.’ The market has decided that workers don’t want to go back to work for less than $15 an hour,” said Ryan Boyer, business manager of the Laborers’ District Council of Metropolitan Philadelphia & Vicinity.

The White House, Federal Reserve, and many independent economists say the inflation increases are likely temporary and come from unique factors around the pandemic. Supply chains are struggling to crank up fast enough to keep pace with the country’s rapid reopening, creating a mismatch between supply and demand. And inflation measures are comparing today’s prices against those from the depths of the pandemic last summer.

“Of course I’m worried, but what we’re hearing, and I believe it, is that this is a temporary and spotty thing and it happens because of bottlenecks when you reopen an economy,” said U.S. Rep. Matt Cartwright (D., Pa.), a top Republican target who represents a Trump-friendly district around Scranton.

So far, none of the Republican critiques appears to have stirred the level of fervor that met the Affordable Care Act and foreshadowed the GOP’s midterm romp in 2010.

American Bridge, the Democratic political group, recently polled women in four swing states, including Pennsylvania, and found economic concerns were “issues one, two, and three,” Floyd said.

“This is a once-in-a-lifetime opportunity for Democrats to be talking about things that we’ve done,” she said. “They’re wildly popular.”

The “hard infrastructure” in the bipartisan deal for roads, bridges, airports, and broadband had 70% support in a national Monmouth University poll released last week, including 51% “strong support.”

The March rescue plan had support from 62% of adults, and the “human infrastructure” proposal for child care, health care, paid leave, and other programs had similar backing.

“I can’t tell you how grateful the mayors of Wilkes-Barre and Scranton and Hazleton were when we announced what they would be getting out of the American Rescue Plan,” Cartwright said.

He, Wild, and other vulnerable Democrats have aggressively promoted the child tax credit and “earmarked” funding for local programs and projects to address needs ranging from addiction to job training to policing.

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“The child tax credit is a game changer,” Wild said.

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Wild now hopes the infrastructure package can boost economic growth, saying she regularly hears from manufacturers “who just want to be able to get their goods out the door.”

As she tours her district this month, she’ll get a firsthand look at whether voters agree with the approach.