The Democrats know they cannot win an impeachment trial, until and unless the GOP invited the impeachment (ala Watergate).
In my view, that only happens if the indictment makes clear that Trump has been compromised for a long time, and obstructed to protect his relationship as Putin's "bitch."
The GOP will only go for Trump's head if they know politically, the timing/temperature is safe.
Otherwise, the D's will wisely not impeach, and let Trump be the incumbent in 2020.