Because the GOP Senate has proven time and time again they lack integrity, and act as Trump’s servants vs stewards of the nation and US Constitution, impeachment is a non-starter.
Fact.
If and when the GOP Senate decides they can no longer survive as crooked and compromised disciples of Trump, then impeachment makes sense. Yet, as 2020 approaches, the most direct and effective method is a 50 State rebuke of Trump at the polls.
Let the GOP continue to parade Trump as the face of their party. He is who you have become. You will own him forever.