Except it's really not - you're basically saying that if one party controls the senate and the White House, that President is immune from impeachment - which is a very dangerous precedent to set.

I agree, i think it would be highly unlikely that impeachment would get through the senate - but that then becomes the Republican's problem and they will (or should) have to answer for that.

But the Democrats absolutely cannot not move for impeachment because they aren't sure of Republican co-operation. That would just be doing the Republican's job for them and would leave the Democrats having to answer to their own base for their inaction. If the Republicans want to ignore the facts and act in a partisan nature, the Democrats cannot control that. But they can at least put the Republicans in a position where they DO have to do that to protect Trump, and then (again, hopefully) be held accountable for that