Like a Volkswagen Beetle mounted with a V-8 engine, the American economy has a lot more power than it can handle right now, and it’s making a lot of noise. So is President Trump, who takes singular credit for a robust second-quarter rise in the gross domestic product of 4.1 percent, something that hasn’t happened under any other president since … Barack Obama. While Mr. Trump praised himself effusively — he’s good at that, isn’t he? — the stock market seemed unimpressed. Friday’ s announcement that 157,000 new jobs were added in July, a modest gain or perhaps a seasonal glitch, elicited an even more subdued reaction. That’s because if you look down the line, there are few clear reasons to be so enthusiastic.

“Over all, we see this report as supportive of our views that the economy is currently firing on all cylinders,” wrote Bricklin Dwyer, a senior economist with BNP Paribas, after the new G.D.P. numbers were announced. But there was a caveat: Mr. Dwyer said that “growth is likely peaking. Indeed, in our forecasts, [the second quarter] marks a high-water mark for growth.”

For one thing, the initial jolt of the Republicans’ $1.5 trillion tax cuts, mostly for corporations and the wealthy, is wearing off. Corporations have bought back $437 billion of their own shares, which leaves them that much less to invest in new production, or wages. In fact, spending on business equipment slowed.

Then there’s the flattening yield curve, which the St. Louis Federal Reserve ’s president, James Bullard, warns could invert late this year if current conditions persist. That means short-term rates, such as those for two-year Treasury bonds, run higher than long-term rates, like the 10-year bond, a sign of pessimism that is a well-known red flag . Recessions tend to follow an inverted yield curve like a stray cat looking for a meal.