President Trump chats with Chinese President Xi Jinping in Beijing in November. The two could soon be locked in a trade war. (Andy Wong/Associated Press)

Dating to the 2016 presidential campaign, arguably the biggest question about Donald Trump was how he would conduct himself in war. Even people who liked his general disposition worried that he would be a loose cannon when lives were at stake. On who was best to handle nuclear weapons, Americans preferred Hillary Clinton by 22 points.

We may soon get a taste of Trump at war — well, trade war, at least.

Trump announced Thursday that he would impose a 25 percent tariff on steel imports and a 10 percent tariff on aluminum ones. The announcement was made despite the reservations of advisers and of top congressional Republicans, and there is a broad sense that it will stoke a trade war with China and others.

In fact, Commerce Secretary Wilbur Ross has said we are already at war; Trump just seems to have launched his first salvo.

It may seem trivial to compare a trade war to a real one, but trade war comes with potentially serious and unpredictable results as well — especially when Trump is involved. And even beyond that, it could preview how Trump might conduct himself in actual military conflict, in which his tendency to retaliate and counterpunch with increasing force would be highly consequential.

Here’s how CNBC described the possibility of a trade war with China and the European Union:

The EU is targeting products with political punch, revisiting a list compiled during George W. Bush-era trade disputes of symbolic American brands.

Potentially in the EU's sights: items such as Harley-Davidson motorcycles, whose corporate headquarters is in House Speaker Paul D. Ryan's home state of Wisconsin. Bourbon is another target, having enjoyed a surge in exports to the EU. Senate Majority Leader Mitch McConnell's home state of Kentucky exported $154 million worth of bourbon to the EU, up from $128 million in 2016, according to data from the International Trade Commission.

Agriculture products such as cheese, orange juice, tomatoes and potatoes are also targets for retaliation.

“The EU stands ready to react swiftly and appropriately in case our exports are affected by any restrictive trade measures from the U.S.," a European Commission source tells CNBC.

The counterpunch from China could land harder because of the scale of trade between the two countries and the reliance of American farmers on China as an export destination. China's Ministry of Commerce is already investigating whether to limit imports of U.S. sorghum, a cereal grain used to feed livestock, in response to previous tariffs from the White House on solar panels and washing machines.

Nicholas Lardy, a senior fellow at the Peterson Institute for International Economics, called the sorghum investigation a “shot across the bow,” and expects more reaction from China when the steel and aluminum actions are unveiled.

As The Washington Post’s David J. Lynch and Damian Paletta report, Trump’s move Thursday was especially provocative because it came even as Liu He, one of Chinese President Xi Jinping’s closest aides, was in Washington to talk to White House officials about preventing exactly the kinds of tariffs Trump just announced.

Trump hasn’t signed the tariffs and won’t do so until next week — a period of time during which it’s not out of the question that he’d shift course. But assuming he presses forward, all eyes will be on the Chinese and the Europeans to retaliate. If and when they do, it’s not difficult to see Trump considering it a personal affront — a dare to escalate things even further. In June, first lady Melania Trump explained that her husband “will punch back 10 times harder” when he’s hit. It's a style that dates to Trump’s formative years and Roy Cohn, his notorious political ally and lawyer.

It’s a style Trump has applied to political debates and his personal feuds — often to great effect. But he hasn’t faced huge decisions about escalating responses in wartime. He has overseen the war in Afghanistan and the fight against the Islamic State, sure, but in neither case are we dealing with powerful state actors. China could inflict real economic damage on the United States if it wanted to, and the increasingly powerful Xi could do it basically at the drop of a hat.

If he did, how would Trump react? It’s an answer that basically nobody knows the answer to, but it’s one we’ve wondered about for a long time. And it could have a much broader application than just on U.S. trade policy.