So why worry? Here’s why. For one thing, last year’s widely applauded synchronous expansion—virtually all advanced economies simultaneously growing at relatively rapid rates—is no more. European economies are growing at a rate of only about 1.6 percent, about half of that in 2017. China is easing monetary policy to cope with a slowdown. Japan’s economy is shrinking. Italy is doomed to perpetual high unemployment and nil growth so long as it remains entrapped in euroland, and might prove unable to service its enormous pile of IOUs. If so, the E.U. banking system that holds its debt might confront the day of reckoning it has so far avoided.

For another, some of America’s reasons for optimism make good headlines, but don’t survive closer scrutiny. The OECD and other high-end forecasts for the near-term reflect the effect of the Trump tax cuts, the impact of which might not prove enduring. Indeed, there is a real danger that the cuts will not generate the additional tax revenue that the administration predicts. If so, already-high deficits will rise, driving interest rates to recession-inducing levels.

Then there are the problems emerging in credit markets. Banks, eager to make new loans to boost their profits, are relaxing their credit standards in a competition for new borrowers. Credit-card and auto loans more than 90 days delinquent are on the rise. Regulators are issuing more warnings to banks to tighten standards than they did last year.