Trump has long been infamous for his Twitter use. The earliest stages of his presidency were marked by his persistent jawboning of large corporations. Many onlookers were dismayed that such tweets would occur daily for the remainder of his four years in office.
As an example, in January 2017, Trump used his Twitter account to propagate negative stories and opinions about General Motors Co. (NYSE: GM) and Toyota Motor Corp. (NYSE: TM) for having manufacturing bases in Mexico. He also praised Fiat Chrysler Automobiles NV (NYSE: FCAU) and Ford Motor Co. (NYSE: F) for hiring more Americans, and exerted pressure on U.S. and foreign companies to "refrain from producing goods in Mexico intended for the U.S. market." Trump also targeted Comcast's (NASDAQ: CMCSA) subsidiary, NBC (BKK: NBC), to suggest that it be subject to a congressional probe.
Trump's Tweets created a new form of market volatility. Experts noted the companies that Trump targeted saw their stocks fall after his tweets, but rebounded quickly afterwards.
Trump's Twitter-targeting of corporations has gradually declined since his inauguration. But, as seen in the decline in Wells Fargo's (NYSE: WFC) share price in the wake of tweets about how their fines and penalties won't be forgiven, Trump's comments on stocks do still carry market influence. And Trump has not entirely stopped using Twitter to post controversial material. Trump has recently made comments about an early retirement for Deputy FBI Director Andrew McCabe, repeating allegations that recent news coverage about him was false, and retweeting images of him in a victory pose over a defeated CNN.
Trump's anti-McCabe comments are based on growing anti-McCabe sentiment amongst Republicans in Congress. These proponents cite a conflict of interest between McCabe and the current administration, based on the fact that McCabe's wife accepted funds from a pro-Hillary donor for her own political campaign. Republicans are thereby acting on the inference that the McCabes harbored anti-Trump sentiment during the 2016 presidential election. Although Trump's director of legislative affairs denies these suspicions, many believe that Trump's recent claims of bias in the FBI are deliberate efforts to undermine Robert Mueller's current investigation into Trump's connections to Russian meddling in the 2016 presidential campaign.
Meanwhile, Trump's corporate criticisms continue apace. As of the last few days of 2017, the companies that have been most targeted by Trump via Twitter are Amazon (NASDAQ: AMZN), Ford (NYSE: F), General Motors (NYSE: GM), Facebook (NASDAQ: FB), Merck (NYSE: MRK), and Aetna (NYSE: AET).