President Trump took to Twitter Monday morning, haranguing special counsel Robert S. Mueller III and witnesses to his ongoing Russia investigation. His tweets have become a common morning occurrence, particularly in recent weeks. But legal experts are calling Monday’s missives a newsworthy development that amounts to evidence of obstructing justice. Trump’s first statement went out after Michael Cohen, his former personal attorney who pleaded guilty last week for lying to Congress about the president’s real estate project in Russia. In his tweet, Trump alleged that Cohen lied to Mueller and called for a severe penalty, demanding that his former fixer...