So far, the long-lasting government shutdown in late January of 2019 tanked Trump's approval rating lower than news of the recent Ukrainian bribery/extortion and impeachment proceedings.
We could see Trump acquitted in the Senate, unless public opinion changes. I don't think it will, anymore. The information infrastructure has become almost completely fractured along party lines, exacerbated by foreign agitators and social media echo chambers, and further inflamed by the least truthful president ever to serve.
How can we trust the legitimacy of the 2020 presidential election? Trump has shown that he's willing to stop at nothing to stay in power, as his evading arrest likely depends on staying POTUS. The GOP have shown that they're willing to enable him beyond what anyone once thought possible only one or two presidencies ago. If Trump is not removed from office by impeachment, he will be further emboldened to ensure his re-election in creative new ways. If Trump is not removed from office by impeachment OR the 2020 election, and it takes until 2022 for Democrats to nab the Senate, we're in trouble. Or maybe the Dems never flip the Senate, SCOTUS rules that a president is not only un-indictable, but un-investigatable, and our little democratic republic experiment is donezo. We get Trump or Trump Jr. "winning" 2024, then they unironically quote Palpatine's I AM TEH SENATE line as they abolish the legislative branch or whatever.
Backing up to 2020, the scheme detailed in kleinbl00's WaPo link could very well play out. Joe Biden is unencumbered by a Senate position, but the GOP thinks he's already been thoroughly smeared by accusations inside their media spheres, so they'll probably focus on Booker, Harris, Sanders, Warren. They don't understand that only inside their disinfo bubble has Biden been tarnished, though it is admittedly quite a regrettably large "bubble". I agree that Joe's son, Hunter, should have never agreed to serve on Burisma's board of directors, but if we're investigating nepotism or violations of the emoluments clause, the Trump administration probably overshadows anything prior by roughly an order of magnitude, at least. I'm not a Biden fan, but I'm forced to support essentially any candidate opposing Trump. Regrettable.
I share your despair, bfx. If 40% of the country somehow still supports Trump, I think we have a serious crisis of culture, stemming primarily from a very entrenched and divided information distribution network.
EDIT: Basically anyone who participates in impeachment proceedings discussions get a circledot, because I have almost no one in my face-to-face, everyday, personal life paying close enough attention to this thing. I feel super shitty to in any way to entangle Hubski in some need for therapy that I may have(?), but I repeatedly arrive at the judgement that we are objectively at a type of low point in U.S. politics, driven overwhelmingly by the GOP and Trump. If anyone needs specifics, just pose a relevant question, I would be happy to respond, but it might take me a day or two, apologies. Very busy.