FBI Director James Comey’s testimony Monday that the bureau has been quietly investigating possible links between associates of President Donald Trump and Russian officials since the summer enraged Democrats who already blame him for rattling the 2016 campaign’s closing days. For the first time, Comey confirmed that the FBI had opened a probe into the Trump campaign in July, the same month he called an unusual news conference to announce the agency had finished its investigation into whether Hillary Clinton mishandled classified information — and three months before he scrambled the White House race a second time by announcing that...