Ok, this impeachment inquiry is regarding Ukraine, but sure let's make this comparison if you want to.
Has Warren's campaign held meetings with known Russian foreign agents seeking dirt on her opponents? Did she then lie about this meeting to the American people? Does she have a long history of getting financed with Russian money? Does she have plans to build a multimillion dollar real estate project in Moscow? Did she hire a campaign manager who laundered Russian money? Has her campaign pushed to have the DNC change its platform to remove support of Ukraine in favor of Russian aggression? Did she go on TV and ask Russia to release dirt on her opponent? Have any of her foreign policy advisors attempt to work with Russia for help with her campaign?
The Russian collusion theory wasn't created out of whole cloth. There was a long history of troubling behavior by Trump that warranted such an investigation.