You can't think like that. If this one man's testimony is all they have it's a shaky case. His fervent personal desire for aid to go the Ukraine undermines his credibility. He is up against over half a dozen more senior diplomats and administration officials who have testified there was a clear cut indication from the President there was no quid pro quo.
This man's testimony only matters if it is the first of many to come. Think like Watergate. It's an 18 month haul, and every day, something new and worse came out until it reached a point that even the most loyal party supporters who were in the dark that stayed behind Nixon (like H.W.) eventually abandoned him, and called on his resignation, too.