evidence: Former president Donald Trump has said that, if he is elected for another term, he will impose an across-the-board tariff on all imported products. As is usual with Trump, he doesn’t offer many specifics — and they can change day-to-day. Sometimes he has suggested it would be a 10 percent tariff; another time he floated it as high as 20 percent. He has also indicated that he would impose a 60 percent tariff on Chinese products. [...] Trump’s undisciplined messaging has given Vice President Kamala Harris an opening to argue, as she did in her nomination acceptance speech at the Democratic convention, that Trump would harm middle-class voters. "He intends to enact what, in effect, is a national sales tax," she said. Her figure is a high estimate from a left-leaning group supportive of Democrats, but other economists agree such tariffs would raise prices for Americans. [...] The Trump campaign has cried foul about Harris’s claim that the tariffs are, in effect, a national sales tax. But at least her statement is based on widely accepted economic theory on the immediate impact of tariffs. One could argue over whether the estimate of the impact is correct. As we noted, she embraces a high estimate.