As a few big companies with relatively few employees amass greater market power and profits, less is left over for workers, according to a 2017 working paper by economists from M.I.T., Harvard and the University of Zurich.

As a candidate, Donald Trump spoke about getting tough on Wall Street, fighting corporate consolidation and looking out for “forgotten men and women” — rhetoric that won him the support of some working-class voters who had backed Mr. Obama. But he and his fellow Republicans in Congress have governed like conventional far-right conservatives — going easy on Wall Street, doing little about corporate consolidation, bolstering corporate profits and gutting a range of protections for those “forgotten men and women.”

Last year, Republicans claimed their biggest legislative victory of the Trump era, reducing federal revenue by $1.5 trillion over 10 years by slashing taxes on corporations and wealthy families. The legislation provides generous and permanent tax cuts to rich people in the investor class, including foreigners who own stock in American businesses. Working-class families, by contrast, received minor savings that are set to automatically vanish after 2025. The tax law will widen income inequality and encourage financial excesses by overstimulating an economy that is already nine years into a recovery.

Consider the stock market, which has shot up after the tax cut was enacted; the S.&P. 500 stock index closed at a new high on Friday. Many analysts argue that the market is not overvalued and has room to run — comments eerily similar to what Wall Street’s salesmen were saying in 2007 and 2008. Yet, the market appears to be more overvalued now than it was before the crisis, according to an indicator created by Robert Shiller, the Yale economist who won a Nobel Prize for his work on bubbles in the stock and real estate markets. His data show that the S.&.P 500 stock index has an adjusted price-to-earnings ratio of 32.29, which indicates that investors are willing to pay $32.29 for $1 of corporate profits. In 2007 and 2008, that ratio never reached 28.

Lawmakers and the administration, and even the Federal Reserve, which should know better, are also sowing the seeds for another crisis by unraveling the financial regulations put in place in the last 10 years. In May, Congress voted to roll back parts of the Dodd-Frank law by exempting banks with assets of up to $250 billion, up from $50 billion, from stricter federal oversight. This was supposedly done to help smaller, community banks, but the change was so sweeping that it would leave fewer than 10 big banks under the kind of supervision many independent experts concluded was necessary after the crisis.

In addition, officials at the Fed and other government agencies have proposed relaxing the Volcker Rule, named for the former Fed chairman Paul Volcker, which restricts big banks from gambling with their depositors’ money on high-risk investments . The regulators also want to ease capital requirements for banks, which will increase profits for the likes of Citigroup and JPMorgan Chase by letting them operate with more borrowed money rather than capital raised from shareholders. Last year, federal regulators decided that A.I.G. is no longer a systematically important financial institution, freeing it from the tighter government scrutiny applied to businesses whose collapse could set off a chain reaction of failures. While A.I.G. is smaller than it was in 2008, when it nearly toppled many big banks, it is still a very big domino in the financial system.

Wait, there’s more. Mr. Trump has effectively neutered the Consumer Financial Protection Bureau by handing control of it temporarily to his budget chief, Mick Mulvaney, who has done the bidding of big banks as a bureaucrat and when he was a House member. He has stopped new investigations by the bureau and watered down penalties against lenders accused of preying on borrowers, to the point that the penalties are meaningless. Recently Mr. Trump appointed Kathy Kraninger, who has little experience in consumer finance, as the permanent head of the bureau.