https://www.reuters.com/article/us-usa-trump-twitter/twitter-again-slaps-warning-on-trump-tweet-threatening-force-against-protesters-idUSKBN23U33V >Twitter Inc on Tuesday placed a warning notice on a tweet by President Donald Trump threatening "serious force" against protesters in the U.S. capital, the second time it has used the label since it began challenging Trump's tweets in May.