To not impeach for something as egregious as this--far eclipsing Tricky Dick's foibles--would be tantamount to admitting to history that the rule of law is now dead. If there is any desire to hang onto democracy, this must be done. Even if it is a certainty known beforehand that no conviction would obtain.
It's already bad enough what's going down in US politics. Throwing up one's collective hands in the name of political expediency only gives license to those who would use the precedent ever after, and embolden the US's enemies. There are things *worth* fighting for, even when the odds are against. Not following through now would to some extent warrant for the Democrats the moniker, "Do Nothing Dems."