I’ve known Mark Zandi a long time — 25 years — and I’ve known almost that long that he’s smart, reasonably apolitical, and a winning combination of calm and kind. He’s how you’d want to stay if you and a school friend started a company and built one of the biggest economics consultancies on Earth.

This week, I found out just how much my mild-mannered source really dislikes Donald Trump, or at least his economic plan.

As Trump prepares to accept the Republican nomination for president this week, the securities markets are turning their attention to what this dog might do to the car (the economy, in this analogy) if he actually catches it. The news isn’t pretty, and the worst vibes aren’t coming from Democratic ideologues.

“ “How would [Trump’s] policies not result in a much-diminished economy?” ” — Mark Zandi, chief economist of Moody’s Analytics

About 400 of 650 institutional investors surveyed by Morgan Stanley said Trump would materially change their markets in the first months of his presidency. They think he might hurt the dollar, tank stocks and hurt Treasury bonds at a time of an ongoing, global investment drought that will worsen thanks to Trump’s proposed tariff barriers against China and Mexico. That’s even as the Federal Reserve raises interest rates to preempt the inflationary effect of a tax cut adding $9.5 trillion to the national debt. Other banks are coming up with similar surveys.

And then there’s Zandi’s analysis, which was so far out of character that it was impossible to miss.

“The economy will be significantly weaker if Mr. Trump’s economic proposals are adopted,” Zandi and three colleagues write. “[If] all his stated policies become law, the economy suffers a lengthy recession and is smaller at the end of his four-year term than when he took office. 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. During Mr. Trump’s presidency, the average American household’s after-inflation income will stagnate, and stock prices and real house values will decline.”

Other than that, Mrs. Lincoln says “Thumbs up!”

The verdict is much the same at Oxford Economics, which has the recession beginning next year and costing the U.S. 3 million jobs. That’s worse than the 2.8 million lost in the 2001-2003 recession. Incomes would shrink and unemployment would hit 7.6% by 2019 — two years sooner than Zandi’s model forecasts 7.3% joblessness.

Trump will obviously say something different on Thursday night — if he talks economics at all.

The point here is that forecasts are less important than who makes them.

As a routine matter, disregard forecasts from political campaigns. Their incentives to puff are obvious. Most people don’t think much more of Washington think-tank reports. Some are better than others, but think-tanks depend on grants — and on the right side of the aisle, distortions coinciding with grantors’ beliefs or interests have gotten much more obvious as Washington’s divisions sharpen.

RNC Chairman Priebus on relationship with Trump

Definitive calls from business economists and market players are wake-up calls because their authors get paid, in repeat business and investment returns, for being right. Business forecasters are fallible, but they’re more insulated from pressure to spout party-line nonsense.

But mostly, the sharpness of Zandi’s call grabs me because it runs so contrary to what I’ve seen covering him over a quarter-century. Being the tough guy isn’t him.

Indeed, the book on Zandi is that he’s too nice. Call him with dumb ideas, and he’ll point out the limited data supporting you. His forecasts often run optimistic, too. For example, Moody’s online tracking of second-quarter data says the economy grew 2.8%, versus the Atlanta Fed’s 2.4% estimate. He’s given donations to both parties — writing a check to Hillary Clinton in 2015, and advising John McCain in 2008. Both use his arguments — Ted Cruz cited Zandi’s observations about Obamacare threatening small-business jobs during the 2013 government shutdown. One conservative publication in 2014 called Zandi “Washington’s fiscal referee.”

And when he’s wrong he’ll admit it — as when he took back the comments Cruz cited, saying emerging evidence disproved them. In Washington, that makes him rarer than pandas and almost as popular.

His brand is that he’s cordial to everyone, and sees half-full glasses aplenty.

Yet, here he is on Trump.

“We actually gave him the benefit of the doubt on some of our assumptions. It would not have been a fair, honest-broker type of analysis if our results showed anything differently,” Zandi told me. “His proposals result in a $9.5 trillion increase in government debt over the next decade, the loss of 11 million undocumented [people] required to leave the country, and a significant increase in tariffs on China and Mexico. How would these policies not result in a much-diminished economy?”

So when Zandi (like Morgan Stanley’s mutual-fund managers) says Trump would make a mess this big, I listen, because of who and what he is. What voters do is up to them.