Are U.S. companies making more money than ever before, or are they mired in one of their longest profit slumps since World War II? Widely used measures have diverged in recent years, leaving many investors worrying that something is amiss.

Look at pretax domestic profits as measured by the Bureau of Economic Analysis, and it is easy to be bearish. Profits are down 13% in five years, the biggest drop outside a recession since World War II. President Trump’s tax cut has cushioned the blow to earnings, with after-tax corporate...