Donald Trump has said he wants to enact big tax cuts, impose drastic immigration reform, and levy hefty tariffs on goods from China and Mexico. Photograph by Damon Winter / The New York Times / Redux

On Monday, as Hillary Clinton was preparing to fly to Ohio to give a speech portraying Donald Trump as a menace to the country’s financial well-being, Moody’s Analytics, the research firm, published a report on the presumptive Republican nominee’s economic program which claimed that his policies could plunge the U.S. economy into a deep recession.

Whether Moody’s timing was a coincidence, I don’t know. Mark Zandi, the firm’s chief economist and one of the report’s co-authors, is a former adviser to both John McCain and the Obama Administration. It’s fair to assume that Zandi isn’t a Trump fan. Regardless of his motivations, however, the Moody’s analysis is illuminating, because it takes Trump’s various pledges seriously and plugs them into a fairly standard model of the economy. And although some of its conclusions can be queried, the report illustrates what a radical break with past and current policies Trump is proposing and how much damage it could do.

Trumponomics consists of three main elements: big tax cuts that are skewed toward the rich; drastic immigration reform, including the deportation of millions of undocumented workers; and protectionist measures, like hefty tariffs on goods from China and Mexico. The Moody’s report concedes that there is little prospect of a President Trump enacting this program in full. He’d have to deal with Congress, for one thing. And his own commitment to the agenda items that he’s proposed is an open question. But, despite the qualifications, it’s a worthwhile exercise to analyze how things might work out if Trump were to do what he’s promised to do.

In the first half of the report, a section titled “Trump at Face Value,” the authors envision what would happen if Trump enacted his full agenda. It makes for some unpleasant reading. The report predicts that an economic slump would begin in 2018 and last until 2020, with the Gross Domestic Product falling by 2.4 per cent. “This would be an unusually lengthy recession—even longer than the Great Recession—although the severity of the decline in economic activity would be more consistent with a typical recession suffered since World War II,” the report says. “Employment will continue to decline and unemployment will rise into the next presidential term, with the unemployment rate peaking at 7.4% in summer 2021.”

What would cause this calamitous outcome? Usually, tax cuts give a boost to the economy, by stimulating consumer spending. And in the “Trump at Face Value” analysis, this does happen: in 2017, the year the Trump tax cuts take effect, G.D.P. growth rises to three per cent, which is high by recent standards. But that’s only the start of the story. As time goes on, three countervailing factors take hold.

First, federal revenues decline sharply—by about $9.5 trillion over a decade, Moody’s says. Then, falling revenues cause the budget deficit to balloon. And since the tax cuts are financed by additional borrowing, the debt-to-G.D.P. ratio starts to climb as well. Taken together, these developments prompt investors to demand a higher return for holding Treasury bonds. Interest rates rise throughout the economy, and the higher cost of borrowing discourages interest-sensitive spending, such as capital investments by businesses, real-estate sales, and auto sales.

Meanwhile—and this is an argument I hadn’t seen spelled out before—the mass deportation of undocumented workers, who represent about five per cent of the labor force, delivers another big shock to the economy. As firms struggle to find workers to fill the jobs once held by undocumented immigrants, the unemployment rate falls, causing wages to rise. That sounds like good news for the employed, but it also causes the inflation rate to pick up, prompting the Federal Reserve to raise the federal funds rate, the interest rate it controls, more rapidly than it would have done otherwise.

Finally, the imposition of big tariffs—forty-five per cent on Chinese imports; thirty-five per cent on Mexican goods—raises the price of many goods sold in the United States. That gives another boost to inflation, and prompts retaliatory moves from China and Mexico. In the ensuing full-scale trade war, U.S. exports take a hit, further hurting the G.D.P.

Thus, the second half of the Trump Presidency witnesses an economic disaster. Over-all demand falls, firms lay off workers, and the unemployment rate, after falling early in Trump’s term, reverses course and rises sharply. The stock market and the real-estate market both slump. By the end of 2020, when Trump’s first term would end, over-all employment has shrunk by 3.5 million jobs, relative to 2016; household income has stagnated; and stock prices and house values have both fallen. Far from making America great again, the full Trump program has led to four lost years.

Of course, predictions like these depend on the assumptions that go into them and the economic model that spits out the numbers. It’s possible that the bond market would react in a more friendly manner to Trump’s tax cuts than the Moody’s analysis predicts, or that the Fed would hold off on raising the federal funds rate despite another fall in the unemployment rate. It’s also possible—likely, I would say—that the value of the dollar would fall, rather than rise, were Trump elected, making American goods more competitive abroad and offsetting some of the impact on exports that a trade war with China and Mexico would cause.

It’s also conceivable that things would work out worse than Moody’s predicts. Investors might get panicked about the prospect of a Trump Administration and its effect on the nation’s finances and global trade. If that happened, the stock market could tank, interest rates could shoot up, and the new President might face an economic crisis from day one.

That's the worst-case scenario: it depends on investors taking Trump's policy proposals at face value. But even if Republicans retain control of both houses of Congress, a President Trump is unlikely to enact every policy he wants. No President does. In the second half of the Moody’s report, the authors present two more scenarios, titled “Mr. Trump Lite” and “Mr. Trump Goes to Washington.”

In the “Trump Lite” scenario, Trump’s tax cuts are reduced from $9.5 trillion to $3.5 trillion; the number of deportations is reduced from eleven million to six million people; and China and Mexico don’t retaliate after being hit with U.S. tariffs on their exports. Operating on these assumptions, the Moody’s model still predicts a recession: by some measures, a deeper one than in the “Trump at Face Value” scenario. The unemployment rate rises to 8.9 per cent in 2020 and 9.3 per cent in 2021. Because the Trump tax cuts are smaller, the downturn starts earlier and lasts longer.

In the “Mr. Trump Goes to Washington” scenario, the authors assume that a Republican-controlled Congress refuses to enact a fiscal package that would raise the budget deficit. Trump’s tax cuts are limited to a trillion dollars over ten years, and are offset by spending cuts. Trump’s immigration reform is also scaled back, with just 3.7 million undocumented workers deported or choosing to leave on their own. And Congress imposes the tariffs on Chinese and Mexican goods for only one year. With these policies in effect, the economy escapes a recession, but G.D.P. growth is modest, averaging 1.9 per cent over Trump’s four-year term.

Such an outcome wouldn’t be nearly as bad as the outcomes in the other two scenarios, but it wouldn’t be great, either. About 2.8 million new jobs would be created, or about half as many if current policies were continued. The net impact of Trump’s policies would still be negative. “The upshot of Mr. Trump’s economic policy positions under almost any scenario is that the U.S. economy will be more isolated and diminished,” the Moody’s analysis concludes. To be sure, this isn’t the final word on the subject. But it will be interesting to see if any reputable economists emerge to challenge it.