There are several schools of economic thought on why growth has been in the doldrums — but unfortunately, few offer solutions that are viable in an atmosphere of political instability.

For example, Lawrence Summers, the Treasury secretary under Bill Clinton, has developed a theory called “secular stagnation.” The core idea is that the advanced economies of the world, including the United States, have entered a phase where there is too much saving and not enough new investment, keeping interest rates and inflation lower than they should be.

Mr. Summers points out that it costs a lot less to start a company in the internet age than when the only way to make money was through manufacturing. So there’s less investment demand.

With a nod to the New Deal economist Alvin Hansen, who wrote about the relationship between population size and interest rates, Mr. Summers notes as well that population growth in Europe and the United States has steeply declined. Without new workers and consumers coming onto the rolls, there’s an upper limit to domestic profit-making opportunities.

Mr. Summers believes there’s a way out of the low-growth trap. He argues for a major debt-financed infrastructure spending program, coupled with tax reform, policies to address rising inequality (since when income gains go almost entirely to those at the top, it’s hard to get a broad-based rise in consumer demand) and efforts to counter protectionist trade practices.

The thing is, nothing like what he proposes will be possible so long as we have a president whose inflammatory language, egregious actions and administrative incompetence continue to alienate voters and members of Congress. President Trump campaigned for infrastructure spending, but at this point neither Democrats or Republicans are likely to get completely on board. As for the other pro-growth suggestions, the president and his cabinet of billionaires couldn’t care less about inequality and seem to be gunning for a trade war with China. And it’s anyone’s guess whether Mr. Trump has the discipline to negotiate corporate tax reform.

The bottom line is that while Wall Street is happy for the moment, the United States economy isn’t reaching its full potential. A tumultuous Trump administration will have a hard time getting us there.