US President-elect Donald Trump arrives for his Presidential Inauguration at the U.S. Capitol in Washington, D.C., on Friday. (AFP PHOTO / POOL / SAUL LOEB)

A good helmsman helps a sailboat win races, but does a good president help the economy grow faster? I think not, and my opinion is not just because I dislike some of President Trump’s proposals. What I wrote during the 2008 presidential campaign sums it up:

One of the candidates said he would "jump start the economy."I can't remember which one, because I switched to Pro Wrestling for a dose of reality. The image the candidates offer is that of a skilled operator maneuvering the levers of the economy from the oval office. Kind of like someone operating a backhoe, but without the hard hat.

As Robert J. Samuelson observed at the time, "We have a $14 trillion economy. The idea that presidents can control it lies between an exaggeration and an illusion."

The largest part of GDP is consumer spending. Remember how President George W. Bush tried to goose the economy with one-time tax rebates back in 2008? Consumers increased their spending the month they received the rebates, but then cut their spending. The net effect was swamped by the large changes to the economy not tied to the president’s short-term policies.

Housing is highly variable over time, but presidents don’t help much. They cannot bring interest rates down. Short-term rates are dictated by the Federal Reserve, and long-term rates by global capital markets. Federal policy can change the terms of federally-backed mortgages, but the big changes in housing come from employment, incomes, and consumer attitudes.

Business capital spending can be tweaked just a little. Accelerated depreciation and full expensing of small purchases have been used to try to goose business spending. Tax policy can make small changes, especially in the timing of expenditures. But again the big trend is driven by the key business questions: do we need more capacity, and will efficiency improvements justify new equipment? President Trump’s goal of reducing red tape and regulation might be helpful, but those issues are subordinate to the main economic drivers, and they are also slow to take effect.

Foreign trade, and specifically the drop in U.S. exports, was a major factor in slow economic growth in 2016. The largest driver of the change was the rising value of the dollar. A president can have some small impact on foreign exchange rates by talking about future policy changes, as Trump did recently, but exchange rates are driven primarily by national economic growth, inflation, and, for a few major countries, the attractiveness of the currency as a global reserve asset. Paradoxically, if President Trump could stimulate the economy and improve the business investment climate, that would push the Greenback up, partially negating those impacts.

A president’s impact comes not from managing the business cycle over a couple of years, but through long-term changes. Think of Lyndon Johnson’s war on poverty, which has impacts on the economy lasting through today. Or Ronald Reagan’s support of Paul Volcker’s inflation-fighting Federal Reserve, which similarly has impacts through the present day.

President Trump can influence the economy positively or negatively, but the greatest impacts he makes will be attributed to later presidents. In the near term, the economy’s moves will not be due to the new president’s policies, be they good or be they bad.