There's nothing wrong with performative resistence as long as it's sincere. Democrats should be looking at the letter of the law and show themselves as earnestly trying to hold Trump to that. Did Trump commit "high crimes and misdemeanors"? If so, articles of impeachment. At the absolute minimum it keeps the limited resources of the fuckwits around him partially tied up on dealing with that. If his allies are spending their time whipping votes against impeachment, they're not spending their time getting support for whatever fuckery they're up to next.
It also makes them far more concerned about what things look like after Trump. It's easy to be greasy for Trump when you think he'll let you do whatever you want, and then pardon you if it all comes out publicly. But how unsure of those outcomes do you have to be before you stop doing crimes in his name out of simple self preservation.
The perception that the democrats are soft bitches who won't go legal scorched earth after regaining legislation and investigative power is what will animate this fuckery right up until 11:59.