WASHINGTON — President-elect Donald Trump says renewing tax cuts would turbo-charge investment and boost U.S. economic growth — a pledge that helped propel him to election victory in November.

But new analysis from the Committee for a Responsible Federal Budget, a nonpartisan fiscal watchdog group, warns that extending tax cuts set to expire next year could do almost nothing to grow the economy. That’s a jarring data point for Republicans framing the case to renew the costly legislation as a way to boost an economy that many voters say isn’t serving them.

Most of the measures up for renewal largely benefit individuals and households, including lower income tax rates and an expanded child tax credit. While those are an easy sell to voters, economists caution on the scale of economic dividend they generate. The bigger spur for investment, they say, would be cuts for corporations.

The business tax breaks in the 2017 law Trump signed in his first term aren’t up for renewal. While he vowed to donors and business leaders gathered at the New York Stock Exchange on Thursday that he’d lower the corporate rate to 15%, that pledge is seen as a potentially perilous move with voters and some Republicans disdainful of more aid for big business.

In a statement, Trump transition spokesperson Anna Kelly defended the GDP growth and low prices that followed from the president-elect’s 2017 tax law, saying the cuts “delivered an economic boom and relief for millions of families across the country — and when he makes the cuts permanent, all Americans will benefit.”

The CRFB based its findings on an assessment from the Congressional Budget Office, which had earlier looked at the outcome of not extending the tax cuts. That nonpartisan arm of the legislature had found that letting the reductions expire would generate a major boost to public finances, reducing the cumulative fiscal deficit by $3.7 trillion over a decade.

Those bigger revenues would mean less public borrowing, in turn offering a spur to private investment. In the CBO’s analysis, that would help make up for a modest reduction in the labor force from the expiration of the tax cuts. “On net, those two effects largely offset each other, resulting in very small changes to gross domestic product,” the CBO said.

That CBO analysis implies that renewing the tax cuts would also have a similar, modest net effect on growth, in the CRFB’s thinking.

Some other models, including those from the Tax Foundation and the Penn-Wharton Budget Model, have shown small amounts of positive economic feedback from renewing the tax cuts — but nowhere near enough to cover the cost of extending the tax cuts, which the CBO projects would amount to $4.6 trillion over a decade.

Still, the outlook from the CRFB and CBO adds to doubts about the ultimate economic gains, and underscores the pressure lawmakers will be under to find savings to fund the tax cuts.

Trump has touted swingeing spending cuts, through a proposed Department of Government Efficiency — a nonprofit group to be run by billionaire Elon Musk and entrepreneur Vivek Ramaswamy looking to come up with ideas for deep savings in public outlays. In addition, the president-elect has talked of imposing a tariff of 10% to 20% on all imported goods plus 60% on Chinese products, and promoted that as an offset for tax cuts.

That comes as the fiscal backdrop continues to deteriorate.

The U.S. budget deficit hit its highest since the COVID-19 pandemic years in 2024, propelled by increased debt interest costs and higher Social Security and defense spending. The shortfall for the fiscal year that ended Sept. 30 came to $1.83 trillion, up from $1.7 trillion the previous year, making it the largest on record aside from the 2020 and 2021 fiscal years.

Since then, new figures show the U.S. ran a $624 billion deficit in the first two months of the current fiscal year, equating to borrowing of $10 billion per day — or $2.1 trillion on a rolling basis over the past 12 months, according to the CRFB.

“That’s an astonishing sum especially when considering the huge challenges ahead,” according to Maya MacGuineas, president of the CRFB. “If we intend to get serious about fiscal responsibility, we might as well start now.”

Extending the tax cuts are only one part of Trump’s fiscal platform, which includes plans to slash other taxes across the board — such as those on tips and overtime pay, along with the corporate-rate reduction.

Investors are watching closely for any signs of emerging fiscal stress. While Wall Street economists say extending the tax cuts would be positive for growth, they caution there are other dynamics at play too.

“It would be crucial for Trump 2.0 and Congress to complement the tax cuts with spending cuts,” said Stephen Jen, chief executive of Eurizon SLJ Capital. “It’s not just about tax cuts, it should be about a small government, which means lower spending.”

That means there’s less room for broader tax easing given the worsening fiscal outlook, according to David Seif, chief economist for developed markets at Nomura.

“If I’m wrong and there are further tax cuts, I doubt that there will truly be many pay-fors. I would instead expect reconciliation instructions to allow for a larger deficit,” he said, referring to the budget reconciliation process that Republicans are planning to use to pass the tax legislation, which will allow them to bypass the need for any Democratic support.

However the debate plays out, the underlying economic landscape of lingering inflation, a surging deficit and potential for slower economic growth all stacks up to a very different starting point to the last time major tax cuts were debated. Martha Gimbel, executive director of The Budget Lab at Yale and a former White House economist under President Joe Biden, said that makes for an uncertain outcome.

“Policymakers need to remember that 2024 is not 2017,” she said. “Similar actions could see very different results.”

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