According to Nate Silver at 538, it's entirely possible that this one act perpetrated by Giuliani and his friends in the FBI was responsible for Trump's win. The impact was measurable in the polling and because it happened so late in the campaign it was impossible to bounce back. Nobody has done Trump a favor as important as that one. Is it any wonder that the Trump 2020 campaign is eager to have Giuliani back, doing what he does best?