Recent presidents have stayed away from trading stocks in companies whose fortunes they could lift or scuttle with the stroke of a pen, but Donald Trump smashed that precedent in the first quarter of this year with more than 3,600 buy and sell orders, many of them involving companies whose profits have been directly impacted by his decisions as head of the government. Among the Trump trades in a recent report filed with a federal ethics agency was as much as $6 million in Nvidia, whose advanced chips Trump approved for sale to China last year. “If he were defense secretary, he would be committing a crime,” said Richard Painter, the chief White House ethics adviser in the George W. Bush administration and a big critic of congressional trading, too.