Or at least starting an impeachment inquiry?
Much of the Democratic establishment's refusal to contemplate taking such a step seems to come from the fear of making Trump look like a harried victim of Dem harassment and thus help him win the 2020 election.
The reasoning is that impeachment hurt Republicans back in the 90s and helped reelect Bill Clinton.
It seems faulty reasoning, since the basis for Clinton's impeachment was his personal behavior, whereas the basis for Trump's would be matters of state, including financial corruption on a massive scale and conspiracy with a hostile foreign state.
The unfair impeachment of Clinton produced sympathy for him and a backlash against his tormentors; an impeachment inquiry against Trump is only going to turn up muck that isn't going to gain him the sympathy of anyone except his rabid base, who seem to be immune to rational argument anyway.
There's also another line of argument, like this, well expressed by Krystal Ball:
The progressive case against impeachment
Impeachment might be a so-so tactic for damaging Trump himself, but it’s a disastrous way to deal with “Trumpism.” And Trumpism is a much graver threat to Americans than Trump himself....
Donald Trump in the White House is not an accident....Look at Australia, Hungary, the United Kingdom, Brazil, Austria — the neo-liberal world order, established and maintained by the United States, is being repudiated in nearly every corner of the world.
Globalization has put workers in a brutal competition against their low-wage, developing world brothers and sisters. Automation is making an increasing amount of that workforce irrelevant. The elite consensus has defined growth as stock market gains and gross domestic product growth, without regard to the fact that the overwhelming beneficiaries of a bull market and increased GDP are big corporations, banks and the 1 percent....
it is toward these underlying forces and grievances that we must focus our attention.
Right-wing populism is on the rise globally because it provides an easy answer to the real, justifiable anger about the neo-liberal world order....
The only way to combat such ideology is with left-wing populism that addresses the real grievances without nativism and racism....
Impeachment would be a distraction from fighting right-wing populism.
Her argument about how Trump is a symptom of a larger problem and not the problem itself is a good one, but it isn't an argument for not starting an impeachment inquiry.
Sure, Dems should fight the underlying forces of Trumpism by promoting "left-wing populism that addresses the real grievances without nativism and racism" — been waiting for the Dem establishment to grasp that point for years now.
And if they do, there's no reason that an impeachment inquiry would be a distraction from it. In fact, it could complement it quite well: This is what the neoliberal elite consensus leads to — oligarchy, financial corruption, and conspiracy among those who've been allowed to grab more than their fair share of society's fruits.
An impeachment inquiry would allow all the Trump administration's dirty laundry to be aired. It would give the Dems a much better chance of getting the information they need than the course they’re taking now. The Trump White House would have less power to block investigations and to hold back revealing documents.
So bring on impeachment, or at least impeachment investigations. There's not even any need to get to the point of the Senate failing to remove. If the investigations turn up what we all know they will turn up, the fact that the Republican Senate still refuses to act as a check on a corrupt POTUS, not to mention by voting to remove him, will look worse and worse for them as the hearings go on and all the nasty Trumpian goings-on and outright crimes are set out for public consumption day after day after day.
So why not impeach, or at least open an impeachment investigation? There seems to be no downside.