Larry Summers, the former Treasury Secretary, appeared Wednesday morning on CNBC, and he laid into Donald Trump’s economic program. Trump’s proposed tax cuts don’t make sense, Summers said, because they would target very high earners, meaning that a lot of the money they free up could end up being saved, rather than spent. And Trump’s infrastructure plans are questionable, Summers argued, because in at least one version of the plans, they depend largely on private financing. The problem, Summers said, is that pension funds and other big investors won’t invest in essential tasks like repairing the nation’s roads, bridges, and airports, because projects like those don’t produce any revenues. So where would the financing for them come from?

Summers’s points, like many of the other criticisms of Trumponomics, are well taken. We know for sure, for instance, that Trump’s proposed tax cuts would greatly accentuate inequality. (“To those who hath, it shall be given,” Martin Wolf, of the Financial Times, quipped this week.) And if those tax cuts aren’t matched by spending cuts, they will run up the budget deficit and increase the country’s already large debt burden. But if the tax cuts instead prompt cutbacks in non-discretionary spending, particularly government investments in education and scientific research, they will undermine economic growth over the long term. Trump’s protectionist impulses, meanwhile, almost certainly won’t bring back lost manufacturing jobs, but they could spark a damaging trade war. And if Trump continues to attack the Federal Reserve, as he did during the campaign, he might well provoke a sell-off in the financial markets, maybe even a collapse in the value of the dollar.

Despite all this, it’s worth recognizing that, in proposing tax cuts and infrastructure spending, Trump, like Ronald Reagan before him, is adopting a bastard form of Keynesianism. And, for the past few years, many Keynesian economists and observers, Summers included, have been arguing that the biggest factor holding back the American economy is a shortage of over-all demand, and that the best way to deal with this would be for the federal government to increase its outlays on things like infrastructure projects, taking advantage of low interest rates to issue more debt. Conservatives and Republicans, by contrast, have argued that it was essential, instead, to reduce the budget deficit and hold the line on spending. When President Obama proposed more infrastructure spending, his requests went nowhere. But he was a Democrat.

The hypocrisy of the Republican Party now potentially embracing a kind of crypto-Keynesian program knows no bounds. But what if this feckless gambit works, at least for a while? What if Trump’s reckless policies, like Reagan’s reckless policies in the early nineteen-eighties, succeed in geeing up the economy, raising the growth rate of G.D.P., and boosting wages and incomes? It might just be a kind of national sugar high, but could it last long enough to help the Republicans retain control of Congress in 2018 and give Trump a platform on which to run for reëlection, in 2020?

This is the nightmare scenario for Democrats—but it’s just one scenario. There is a host of differences between today and November, 1980. For one thing, Reagan was elected following a recession, meaning that there was a lot of spare capacity in the economy. The unemployment rate also stood at 7.5 per cent. Today, we are in the eighth year of an economic expansion, and the jobless rate is 4.9 per cent. Standard economic theory suggests that if you try to stimulate an economy that is already operating at full employment, or something close to it, you will only succeed in driving up interest rates and inflation—the end result is likely to be a recession.

Earlier this year, Moody’s Analytics argued that a comedown from a Trumponomics sugar high wouldn’t be delayed long—a year or two, perhaps—and then we’d face the prospect of a deep slump. “Under the scenario in which all his stated policies become law in the manner proposed, the economy suffers a lengthy recession and is smaller at the end of his four-year term than when he took office,” Moody’s said in a report issued in June. “By the end of his presidency, there are close to 3.5 million fewer jobs and the unemployment rate rises to as high as 7%, compared with below 5% today.” Moody’s also considered a second scenario, “Trump Lite,” in which his tax cuts were reduced from $9.5 trillion to $3.5 trillion over ten years. Even in this case, the analysis predicted a deep recession beginning in 2018. By 2020, the report said, the unemployment rate would be 8.9 per cent.

We can probably assume that Trump wouldn’t get reëlected in four years’ time if the unemployment rate is seven per cent or higher. It should be noted, however, that the gloomy Moody’s analysis depends on a number of assumptions, the most important of which is that the economy is indeed currently operating at full employment. Moody’s also took it as given that Trump would follow through on his pledge to deport millions of undocumented workers, thereby reducing the U.S. labor supply and forcing employers to offer higher wages to attract workers. That might sound like good news for workers, but it would probably prompt the Fed to raise interest rates more rapidly than it would have otherwise. And, finally, Moody’s assumed that Trump would go ahead and impose tariffs on goods from Mexico and China. In addition to starting a trade war, such a policy would raise the cost of imported goods, put more upward pressure on inflation, and provide the Fed with another reason to hurry up and raise rates.

These assumptions may turn out to be reasonable, or they might not. Some economists believe there is more slack in the labor market than the headline unemployment rate indicates. If so, Trump’s stimulus could prompt more discouraged workers and retired people to go out and look for jobs, which, at least for a time, would raise the labor-force participation rate, which might in turn check wage inflation. It is also at least conceivable that Trump will back off his mass-deportation plans. And lately his statements about imposing tariffs have sounded more like a threat, or a bargaining tool, than an actual policy commitment.

At this stage, there remains too much uncertainty about the scope, details, and likely consequences of Trump’s economic program to make reliable predictions. The infrastructure plan that Summers criticized, for one, is just a proposal. If, as some reports indicate, Senator Chuck Schumer, the incoming Democratic Minority Leader, is prepared to negotiate with Trump about the details of his infrastructure plan, things could end up looking very different. On top of that, it is still possible that Paul Ryan, the House Speaker, along with his fellow-Republican deficit hawks, will push to dramatically scale down both the infrastructure plans and the proposed tax cuts. The economists at Goldman Sachs say their best guess is that Trump will end up getting less than half of the infrastructure spending he wants, and less than a third of the individual tax cuts he has proposed.

Another unknown is how the Federal Reserve will react to Trump’s Administration. For the past couple of years, Janet Yellen, the Fed chair, has hesitated to raise interest rates, partly because she sympathizes with the view that there is still some hidden slack in the labor market. Now that Trump is headed for the White House, will Yellen and her colleagues move to raise rates more rapidly, or will they be willing to accommodate a fiscal stimulus?

Finally, it’s far from clear how the financial markets, particularly the bond markets, will react over the long term to a Trump Presidency, and the prospect of larger deficits. In normal times, U.S. Treasury bonds are regarded as a safe haven, which helps keep interest rates, including mortgage rates, low. The times aren’t normal, though. If investors came to believe that the Trump Administration was embarking on a credit binge, or turning the United States into a banana republic, sentiment could change rapidly.

Ultimately, the good name and financial credibility of the United States government depends on faith in the country’s political system. Come January 20, 2017, that system will have at its helm a tax-dodging, self-promoting businessman and reality-television star who, among other things, stands accused of running a fraudulent enterprise—Trump University. Expect some turbulence ahead.