About those market gains.

The second quarter is ending about where it started for U.S. equity investors, with the Dow Jones Industrial Average having eked out a 171-point improvement for the last three months. Without the gains of the last two days, the Dow would have been even flatter.

Still, it's flat enough. The Dow stands at about 24,276, not far from the 24,262 it posted on May 4, or the 24,190 it showed on February 9, or the 24,211 it had back on December 7. It's been more than half a year and, on average, investors in the biggest publicly-traded U.S. companies haven't made a dime.

To be sure, the Nasdaq Composite rose almost 7% for the quarter and the Russell 2000 gained almost 8%, with both recently setting record highs. Investors reckoned that chip and entertainment companies, as well as smaller ones that focus on the domestic market, are better bets as President Trump's trade war looks set to get hotter, along with the climate. For the week, though, the Nasdaq put up its worst showing since April.

Because for big companies dependent on supply chains that stretch around the world, prospects for profit gains amid tariff threats are melting faster than Arctic sea ice. Less than 10 years after the U.S. government rescued General Motors (GM and Chrysler (FCAU through loan guarantees in the middle of the financial crisis, GM said on Friday that U.S. tariffs on imported vehicles could lead to "a smaller GM" and may isolate U.S. businesses from the global market.

"Increased import tariffs could lead to a smaller GM, a reduced presence at home and abroad for this iconic American company, and risk less -- not more -- U.S. jobs," the Detroit-based automaker said in comments filed with the U.S. Commerce Department.

"Combined with the other trade actions currently being pursued by the U.S. Government -- namely the Section 232 Steel and Aluminum tariffs and the Section 301 tariffs against Chinese imports -- the threat of additional tariffs on automobile imports could be detrimental to our company. At some point, this tariff impact will be felt by customers," GM said.

The U.S. is reportedly considering a 25% tariff, and the president said in a Tweet on Tuesday that the administration is concluding a study of tariffs on cars from the E.U.

GM fell as much as 2.1%, while rival Ford Motor Co. (F lost 1%. Auto parts suppliers also fell, with American Axle (AXL down 1.1% and Lear Corp. (LEA off by 0.8%.

GM's complaints come in the same week as a company that President Trump used to count as one of his favorites, Harley-Davidson (HOG , said it would move some production overseas so that its European customers wouldn't have to pay $2,200 more for a motorcycle imported from the U.S. The president complained, but Harley sells about 40,000 motorcycles a year to Europeans, and accessing overseas markets is part of how Harley is trying to run its business.

It looks as though there is more to come in the global tit-for-tat, a pointless exercise for everyone concerned except for the President of the United States and perhaps the autocrat in the Kremlin, which has an interest in weakening the economic power of the Western democracies. On Friday, Canada announced $12.6 billion in retaliatory tariffs on U.S. goods in response to the U.S. tariffs on steel and aluminum imports.

Next week Trump plans to hit China with $34 billion in tariffs on her exports, a sum that China plans to match regarding imports from the U.S. Among the hardest hit may be soybean farmers in states including Ohio, Iowa, Indiana and Missouri, who sell about a third of their exports to China.

However, this strategy is said to be satisfactory to the administration because it reckons that because the trade difference favors the U.S., Americans will be better able to put up with the loss of sales and jobs than the Chinese will.

Given the fact that there are Chinese consumers (as well as political leaders) today who have lived through Tiananmen Square, the Cultural Revolution and the Great Leap Forward, the hope that the Chinese command economy will knuckle under before American consumers, farmers, bankers or industrialists -- or politicians -- do may be far-fetched. Still, that's the plan.