If history is a guide, the odds that the American economy is falling into a double-dip recession have risen sharply in recent weeks and may even have reached 50 percent.

Economies have a strong self-reinforcing nature. When people are optimistic, they spend, which begets hiring and then more spending. When people are anxious, they pull back, which leads to a cycle of hiring freezes and further anxiety that often lasts for months.

The United States appears to have entered some version of the vicious cycle. Most ominously, job growth has slowed to a pace that typically signals the start of a recession.