Then-Senate Democratic leader Harry Reid released a letter in the heat of the 2016 election alleging Trump-Russia collusion even though the CIA director at the time urged him not to, according to a person familiar with their conversation. Mr. Reid’s Aug. 27 letter to the FBI appears to mark the first time a Democrat officially accused President’ Trump’s campaign of colluding with the Russian government to hack his party’s computers. The letter has come to represent for conservatives the “deep state” — Obama loyalists leaking unproven allegations to the press against Mr. Trump and his people to ruin the campaign,...