Shokin was shaking down Mr. Zlochevsky and Burisma. Shokin used the threat of prosecution to try to solicit bribes from Mr. Zlochevsky and his team. Ziochevsky is a corrupt official from the pro-Russian President Viktor Yanukovych. Shokin was actually undercutting the UK investigation per Shokin's deputy Kasko, and the US diplomatic corps wanted Shokin out. Kasko resigned because of lawlessness in the Prosecutor's office. Shokin's resignation was spurred by protests and Joe Biden's threat.
The Impeachment is a de facto sealed indictment. Pelosi may hold on it through most or all of 2020, which increases the possibility of a Biden election.
If we had cut bait on Trump a long time ago, Dems would be nominating Warren, and Pence would prevail. The longer this drags on the greater potential of Trump fatigue