NEVER before had 140 characters caused such a market stir. On December 12th 2016, just weeks after being elected America’s 45th president, Donald Trump took to social media to attack Lockheed Martin, a weapons-maker. “The F-35 program and cost is out of control,” Mr Trump tweeted to his 25m followers, referring to the defence contractor’s stealth fighter jet. “Billions of dollars can and will be saved on military (and other) purchases after January 20th,” he added. Within minutes of the opening bell, Lockheed’s share price plummeted 5%, wiping out $3.7bn of market value. Shares in defence firms General Dynamics, Raytheon and Northrop Grumman fell 3-4%, together losing $4.6bn in value, before quickly recovering.

Such market-moving statements have become a regular occurrence during the Trump era. On the campaign trail, Mr Trump’s late-night tweets frequently targeted “crooked” political opponents and “dishonest” media outlets like the New York Times. But since the election, it is publicly traded companies that have often incurred the president’s wrath. Manufacturing firms—particularly those planning to shift operations overseas—have been on the receiving end the most. America’s “big three” carmakers (Ford, General Motors, and Chrysler) have been mentioned in the president’s tweets more than half a dozen times.

Market reactions to the Tweeter-in-chief have been swift. On January 5th, after Mr Trump complained about Toyota’s plans to build a plant in Mexico, shares in the carmaker fell 3% in the first minute of trading. A few weeks later, following an enthusiastic tweet about meetings with the bosses of Ford and General Motors, their share prices immediately jumped 1% and 2.5% respectively. On average, the shares of publicly listed companies have risen about 1% following a positive tweet from the president. Negative tweets have corresponded to declines of a similar magnitude. Such gains and losses, analysts point out, are short-lived. But this is true of any market news. Traders hoping to profit from Mr Trump’s pronouncements will have to be quick.