President Donald Trump's trade war began almost one month ago, on March 1, when he announced steep tariffs on steel and aluminum that would take effect the following week.

The 25 percent tax on steel and 10 percent tax on aluminum coming to the U.S. from abroad was applied broadly at first, with no specific targets and no quotas. And the president announced them despite being seemingly at odds with some of his key advisors. Former economic policy director Gary Cohn quit the administration over it.

The global reaction was swift and fierce, with condemnation coming from European and other foreign leaders, members of Congress and even captains of U.S. industry. Canada, which exports more steel and aluminum to the U.S. than any other country, threatened to retaliate even as it was in the middle of renegotiating the 24-year-old North American Free Trade Agreement with Mexico and the U.S.

The S&P 500 fell 1.33 on March 1 but rebounded the next day and had retraced its steps by March 5. The markets appeared to shrug off the rhetoric coming from the European Union, which said it could slap new import taxes on American orange juice, bourbon, denim, cranberries, peanut butter and motorcycles.

When he signed the tariffs into effect on March 8, Trump exempted Canada and Mexico and gave other countries the chance to argue why they should also be exempted.The S&P 500 rose 0.45 percent and 1.74 percent on March 8 and 9 before beginning a four-day slide the following week.

By the end of March, the list of the exempted would grow to include members of the European Union, Argentina, Australia, Brazil and South Korea.

On March 22, Trump signed retaliatory tariffs on up to $60 billion of Chinese imports, including components used in the aeronautics, technology and energy industries. The S&P 500 shed 2.5 percent that day and 2.1 percent the next day and then rebounded 2.7 percent on March 26.

That day, there was word that South Korea had made concessions on imports of American cars, what some called Trump's first major trade deal.

Last weekend, China responded to the U.S. tariffs in kind, announcing new taxes on American imported meat, wine, fruit, nuts, ethanol and other products, not great news for American farmers, who shipped $20 billion in products to China last year. On Monday, the S&P 500 fell 2.2 percent.

On Tuesday, Trump raised the ante. The U.S. Trade Representative released a list of 1,300 product categories covered by the 25 percent China tariffs. It includes parts used to make a variety of household products, from flat-screen televisions to dishwashers, snowblowers and even vaccines. And the stock market appeared to take it all in stride. The S&P 500 closed up 1.2 percent.

Overnight Wednesday, China answered with its own 25 percent tariffs on a still-longer list of American goods, including whiskey, cars and soybeans.

Stock markets are responding negatively to the escalating tensions. European exchanges were down on Wednesday, and the wavered, though it is off its lows for the day. Boeing shares fell 2.6 percent and Caterpillar traded down 1.8 percent, the two hardest-hit components of the Dow Jones industrial average.