Last year, after an earlier stock market swoon brought on by headlines about the U.S.-China trade conflict, I laid out three rules for thinking about such events. First, the stock market is not the economy. Second, the stock market is not the economy. Third, the stock market is not the economy.

But maybe I should add a fourth rule: The bond market sorta kinda is the economy.

An old economists’ joke says that the stock market predicted nine of the last five recessions. Well, an “inverted yield curve” — when interest rates on short-term bonds are higher than on long-term bonds — predicted six of the last six recessions. And a plunge in long-term yields, which are now less than half what they were last fall, has inverted the yield curve once again, with the short-versus-long spread down to roughly where it was in early 2007, on the eve of a disastrous financial crisis and the worst recession since the 1930s.

Neither I nor anyone else is predicting a replay of the 2008 crisis. It’s not even clear whether we’re heading for recession. But the bond market is telling us that the smart money has become very gloomy about the economy’s prospects. Why? The Federal Reserve basically controls short-term rates, but not long-term rates; low long-term yields mean that investors expect a weak economy, which will force the Fed into repeated rate cuts.

So what accounts for this wave of gloom? Much though not all of it is a vote of no confidence in Donald Trump’s economic policies.