If this is how we show China who’s boss, China has just learned it has a pretty dumb boss.

Last Thursday, President Donald Trump signed sweeping new tariffs on steel and aluminum, against the urging of economists, allies and most of the manufacturing, retail and home-building industries. This policy will likely destroy American jobs both in industries that use steel and aluminum and in ones that may soon be hit by retaliatory measures from other countries.

But no matter all that. Trump really, really wants to stick it to China! Too bad this won’t stick much.

U.S. steel jobs have been mostly lost due to technological change (i.e., robots, not China). U.S. aluminum jobs have been mostly lost to places with cheaper electricity (i.e., Iceland, which is coincidentally also not China).

Right now China isn’t even among the top 10 producers of U.S. steel imports. The top country we import from is Canada, which apparently should be grateful it has been given a reprieve from these tariffs “at least at this time.”

If hurting Canada is Trump’s best strategy for intimidating China, our next step should be maple-syrup taxes.

Misdirected metal tariffs are hardly the only way our dealmaker in chief has revealed himself to be a less-than-slick negotiator with China.

The day before signing the tariff proclamation, Trump tweeted: “China has been asked to develop a plan for the year of a One Billion Dollar reduction in their massive Trade Deficit with the United States.”

Golly, a whole One Billion Dollars! That sounds like a Staggering Sum.

Except that our trade deficit with China last year was $375 billion. That means Trump asked China to amend the balance of trade by about 0.3 percent, or the equivalent of less than one day’s deficit. Because duh, everyone knows you prove yourself a tough negotiator by making a ridiculously teeny opening ask.

A subsequent Wall Street Journal article suggested Trump actually meant to demand a $100 billion change in the deficit. For all the internet memes comparing Trump officials to Bond bad guys, the bumbling villains of Austin Powers are the better reference.

Astonishingly, Trump’s $99 billion rounding error wasn’t even the only flub in that short trade-policy-via-Twitter missive. Note the president referred to China’s “massive Trade Deficit with the United States.” Not to be persnickety here, but China has a trade surplus with the United States; we’re the ones with the deficit.

Trump has repeatedly accused administrations of making “bad deals” on trade due to “incompetence.” Yet in one fell tweet, he revealed his own trade-related ineptitude twice. You can bet Beijing noticed.

But forget Twitter for a moment. Had Trump really wanted to get “tough” with China in the name of promoting U.S. interests and values, he has had ample opportunities.

Every time, he has played right into Chinese hands.

Take, for instance, the Trans-Pacific Partnership. This 12-country pact deliberately excluded China; it was to make sure the United States rather than China got to “write the rules of the road for trade in the 21st century,” as then-President Barack Obama put it.

Among Trump’s first orders of business upon taking office, however, was to pull out of the pact. But that doesn’t mean the deal died when we left.

Incidentally, also last Thursday — the day Trump signed his metal-tariff proclamation — the remaining 11 members of the pact signed a new version of the same trade deal. Their version stripped out some of the conditions won by U.S. negotiators, such as increased intellectual property protections for pharmaceuticals.

Trump has declined other chances to get tough with China.

After it became clear the Chinese constitution would change to allow President Xi Jinping to hold power indefinitely, Trump didn’t criticize the authoritarian move. Instead, in comments secretly recorded at a fundraiser last weekend, he expressed admiration for Xi as “a great gentleman” who “treated us tremendously well when I went over there.” Xi, Trump cheered, had just made himself “president for life. … I think it’s great.”

Trump jokingly added that “maybe we will give that a shot someday,” the line that got the most attention. But the comments letting Xi off the hook, in fact praising Xi for consolidating power, were far more consequential. They signal to China that not only do we not care about the country’s increasing authoritarianism; we encourage it.

It’s not altogether surprising, though. Xi has charmed the pants off Trump, who appears envious of the Chinese government’s military parades, press controls, disregard for human rights and other totalitarian perks.

China’s most dangerous possible export to the United States isn’t a metal. Increasingly, it’s a style of political leadership.

Email Catherine Rampell at crampell@washpost.com. Follow her on Twitter: @crampell

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