To impeach Trump, you would need a super-majority (2/3). That means 67 total senators. There are 46 Democrats, and 2 Independents. Assuming you had 100% support of the Democrats and Independents, you would still require 19 Republican Senators to side with the Democrats and Independents.
When was the last time 19 Republican senators crossed the aisle (ie, on a partisan issue) and joined or largely unified Democratic party?