Richard Nixon
The history of impeachment proceedings in the modern era, from Nixon to Clinton to Trump, shows that a successful impeachment needs three things: it must be bipartisan, it must be about something Americans think is important, and Congress must strike while the iron is hot. In Trump's case, Democrats have botched all three.
First, this impeachment inquiry is an entirely partisan affair. The public hearings of recent weeks have made this undeniable, but even before the hearings it was obvious that Democrats alone were going to conduct this impeachment. The House's impeachment inquiry resolution passed last month without a single Republican vote, and in fact two Democrats joined GOP lawmakers in voting against the resolution, making opposition to the impeachment probe bipartisan.
House Speaker Nancy Pelosi tried to avoid this, which is one reason she refused to call for an open House vote on whether to open an impeachment inquiry and instead announced the "inquiry" in a press conference. She knew any House vote would be entirely along partisan lines, undermining the inquiry's credibility from the outset. By the time Democrats brought forward their impeachment rules resolution at the end of October, Pelosi had lost control of the process.
Comment: It is also clear that, on the heels of the ridiculous and disastrous "Russiagate" and Mueller investigation - there is already a precedent set in the minds of many Americans for Washington accusing Trump of great malfeasance and, after much hoopla, it coming to absolutely nothing. This impeachment probe is just obviously more of the same. Unless you're a Trump hater that is.