Companies in the S&P 500 Index bought $3.5 trillion of their own stock between 2010 and 2016, almost 50 percent more than in the previous expansion. The pace has slowed in the last two years. The tax bill could kickstart it.

Buybacks have fueled the stock rally (there’s disagreement about how big a part they played). And the rally’s biggest benefits go to the richest. On Twitter last week, Trump invited his followers to check their swelling retirement accounts. Only about half the country’s households have any such nest-egg.

Soaring markets helped the top 1 percent of Americans increase their slice of the national wealth to 39 percent in 2016, according to the Fed’s Survey of Consumer Finances. The bottom 90 percent of families held a one-third share in 1989; that’s now shrunk to less than one-quarter.

Republicans are gambling that they can run the economy so hot that companies will hire more workers, and eventually boost their wages. There’s a strong argument that the private sector can train them better than government programs can.

‘Benefits Everybody’

“The more growth we have, the more that benefits everybody,” said Ike Brannon, a former Bush administration Treasury official who’s now president of Capital Policy Analytics, a consulting firm. “It forces businesses to train people at the fringes.” He points to the late 1990s, when growth averaged more than 4 percent and the poorest one-fifth of households saw substantial income gains.

Looming in the background then was a technology-stocks bubble. It burst in March 2000, plunging the economy into recession. What happened next is telling -- it illustrates the perverse asymmetry of bubbles. In the following three years, those poorest households saw their incomes fall more than twice as much as their richest counterparts.

The pattern was repeated after the even bigger housing crash of late 2007. Today, even after an increase of more than 9 percent over two years, incomes at the bottom are short of pre-crisis peaks, while higher earners have comfortably surpassed them.

Companies flush with cash are using it to buy more customers via mergers, or reward capital through dividends, according William Spriggs, chief economist at the AFL-CIO, the country’s biggest labor union group. But American workers won’t put up with any more business cycles that yield them few gains, he says. “This is the last time they can get away with it, because the backlash is going to be huge.”

In the end, the trend toward inequality amounts to capitalist suicide, Spriggs argues. Companies need demand, which requires rising wages so that workers can afford goods and services. “Businesses can’t create themselves, they respond to general growth in income,” he said. “Inequality chokes off business development.”