Why Do the Dems want to Impeach the President?

Do I understand this correctly? The Democrats want to impeach President Trump for pressuring the new Ukrainian President to investigate Joe Biden pressuring a previous Ukrainian president? Don’t the Democrats know if they investigate President Trump pressuring the new Ukrainian president, Joe Biden’s dealings with a previous Ukrainian president will also be exposed? Maybe that’s what they want. The Dems wouldn’t let Joe Biden run against Hillary Clinton. Maybe they don’t want him running against Elizabeth Warren either.

Sounds like the investigations of Trump colluding with the Russians. The Obama administration’s allegation of Trump colluding with the Russians was based on dossiers obtained from Hillary’s collusions with the Russians.