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Overnight lending rates among financial institutions are a mechanism by which central banks carefully tune the pitches of their economies. In the U.S., the benchmark rate is 2.25%, with an incremental reduction anticipated next week.

President Donald Trump, meanwhile, is a confident-seeming man who dispenses advice through a medium ill-suited to complexity, as he did on Wednesday when he tweeted that the “Federal Reserve should get our interest rates down to ZERO, or less, and we should then start to refinance our debt.” The Fed’s governors are “boneheads” not to have done it already, he typed.

Well, that’s fun, but let’s unpack it.

Trump has called himself the king of debt. “I love debt,” he told CNBC as a presidential candidate in 2016. “I love playing with it.” He’s worried, however, about the amount of interest the U.S. pays on its $22 trillion national debt (although not so much that he wouldn’t toy with a higher burden for the sake of tax cuts).

He’s also taken note of central-bank action in places like Europe, where rates were dropped further below zero on Thursday to counter moribund growth and uncertainties including Brexit. Following that news, Trump again accused U.S. central bankers of tootling.

The idea behind negative interest rates is that making banks pay to store cash will persuade them not to keep more than is required in reserve, instead lending that money out so it can go to work in the economy. It’s a theory that only in recent years has been put to real-world tests. In practice, there have been counterintuitive responses that have muted the policy’s effectiveness.

Trump has long argued for lower interest rates, except when he’s argued for higher ones. On this as with other matters, he’s wildly improvisational. It’s worth noting that the best improvisers in any field become so only after first mastering the fundamentals. Despite his self-perpetuated reputation as a maestro of the music of business, it’s not clear that Trump can play a basic scale.

Refinance the nation’s debt at no cost, or better yet, get paid for it? Sounds good, but why should current bondholders give up safe payouts as high as 7% years before an issue comes due? The federal government cannot “call” bonds before their maturity dates as most municipal and some corporate issuers can.

Make America muy bueno again? Not if lower rates tempt consumers to rack up additional credit beyond their means, or if institutional investors are encouraged to boost returns by taking risks they wouldn’t otherwise, or if the Fed is left without proven strategies in the next downturn.

That’s not to mention the ordinary Americans who’d like at least some return on their savings but who don’t appreciate the volatility of the stock market. Or who’d face higher fees on their banking activities as institutions sought ways to counter squeezed profit margins. JPMorgan Chase CEO Jamie Dimon, thinking ahead to the possibilities, said that’s what executives at his banks have discussed doing.

No, if the U.S. benchmark rate ever again drops to zero, it’ll be the work of an independent Fed, acting out of dire necessity. As David Wessel, director of the Hutchins Center on Fiscal and Monetary Policy, was quoted as explaining in the Washington Post: “The president is calling for what essentially are emergency monetary policy measures at a time when unemployment is at a 50-year low, the U.S. economy is doing better than its peers’ and is still growing.”

So, not now. In the meantime, aspiring armchair economists: practice, practice, practice.