Donald Trump’s selection of JD Vance as his running mate cements the Republican party’s shift from the free-market conservatism of the Reagan and Bush eras to the economic populism of the Make America Great Again movement.

And if they win in November, the impact of the Trump-Vance economic agenda on everything from global trade to corporate taxes could be huge — and unsettling for US business and allies.

“People like JD Vance . . . are just being realistic about the 21st century global economy — it has different challenges than the challenges of Ronald Reagan’s economy,” said Nick Iacovella from the Coalition for a Prosperous America, a think-tank.

But what will Maganomics actually do?

More trade wars?

Trump’s disdain of global commerce has become more pronounced since he left office, and is shared by Vance. The former president proposes a sweeping 10 per cent tariff on all imports, plus a 60 per cent levy on goods from China.

Trade tensions with European and Asian allies, and possibly even Canada, will flare up again, believe analysts. Trump also wants a weaker dollar to help boost exports, which could bring friction on currency policy with trading partners.

During his first term, Trump’s trade battles were blustery but erratic: he alternated threats and punitive measures with efforts to negotiate bilateral deals, including with China. He managed the domestic fallout by subsidising some victims of retaliatory counter-tariffs, including farmers in states such as Wisconsin — the swing state hosting the Republican convention this week.

There were some divisions even within Trump’s own administration about how far to go on tariffs, as well as resistance from some Republicans on Capitol Hill.

But the Republican party is these days much more aligned with Trump’s anti-globalisation views on trade, and has embraced his plans to crack down on immigration. US business will be wary of both stances, fearing a loss of foreign markets and immigrant workers.

“The main thrust of the postwar American order of globalisation has involved relying more and more on cheaper labour. The trade issue and the immigration issue are two sides of the same coin,” Vance told The New York Times earlier this year.

How far will the tax cuts go?

Lowering taxes has been a pillar of Republican economics for decades. In 2017 a Republican Congress and Trump enacted a sweeping $1.7tn package of corporate and individual tax cuts.

They are set to expire next year, unless Trump makes them permanent. He also wants to cut the corporate rate from the current level of 21 per cent.

Democrats say the plan is another massive giveaway for the rich. So Republicans want to structure the package to be less brazenly beneficial to the wealthiest households and businesses. Vance has expressed doubts about some of the tax cuts.

“I don’t think this is going to be a straight extension, there will be some competing visions,” said Doug Holtz-Eakin, director of the American Action Forum, a right-leaning think-tank. “There’s been open talk of perhaps even raising the corporate rate, because we don’t care about big companies, and using that money to pursue other objectives.”

Another question hangs over the billions of dollars of tax breaks passed by President Joe Biden to boost domestic manufacturing. The measures — especially those for clean energy — have been criticised by Republicans. But many parts of the country are benefiting from the new jobs, and Republicans are increasingly sympathetic to a notion once considered anathema in the party: American industrial policy.

“They didn’t vote for them. They didn’t design them, but a lot of their constituents are getting them. We’ll see when the rubber hits the road just how easy it is to remove some of them,” Holtz-Eakin said.

For or against business?

The Republican convention gave a prime spot to an unexpected speaker on its opening night this week: Teamsters union boss Sean O’Brien. He bashed big business, with Trump and Vance sitting yards away.

“Remember, elites have no party, elites have no nation. Their loyalty is to the balance sheet and the stock price at the expense of the American worker,” he said.

It is unlikely that Trump will suddenly embrace unionisation or labour rights but O’Brien’s appearance shows how Republican support for big business and large multinationals as beneficial job creators is no longer a given.

The fury at corporate America in recent years has largely been directed at their promotion of progressive social goals, fuelling stand-offs such as the one between Florida governor Ron DeSantis and Walt Disney, the media group.

But a recent FT-Michigan Ross poll showed that Americans believe corporations, even more than politicians, are responsible for their economic woes — more fodder for populist leaders.

Trump’s allies and big donors from corporate America are likely to escape his public wrath, but the party’s willingness to directly attack chief executives has grown sharply.

Last month, Josh Hawley, a Missouri Republican senator who shares Vance’s views on business, lambasted Boeing CEO Dave Calhoun for safety lapses at the aerospace group and his pay package. Republicans used to think executive pay was a matter for companies and their boards.

“You’re getting compensated like never before,” he charged.

How loose will regulations be?

Deregulation has been a Republican mantra for years. In some sectors such as energy and climate, a new Trump administration would rapidly try to roll back anti-pollution and anti-emission measures, while promoting fossil fuel production.

But in other areas the answer is not straightforward. Vance has made unusual alliances with the some on the left by supporting the tough antitrust policies of Lina Khan, the chair of the Federal Trade Commission appointed by Biden who is loathed on Wall Street.

Khan is “one of the few people in the Biden administration that I think is doing a pretty good job”, Vance once said.

His stance could especially put technology companies in the crosshairs of a second Trump administration, given the scrutiny they have been getting from competition authorities.

But other sectors could also face a tougher regulatory environment than usual under a new Trump administration.

For instance, Vance has joined a number of Democrats, including Elizabeth Warren, in calling for regulators to claw back pay in the event of bank failures. He has joined Democrat Sherrod Brown, his fellow Ohio senator, in calling for better rail safety protocols after a derailment of a cargo train in the state. He has expressed some admiration for Bernie Sanders, the left-wing Vermont senator.

“The people on the left, I would say, whose politics I’m open to — it’s the Bernie Bros,” Vance told The New York Times earlier this year.