Impeachment is a political procedure not a legal one.
The only ones that could make impeachment/removal a possibility would be the GOPe in the House and Senate, and only if they all joined in. It would lead to each and every one of them being voted out of power. If they succeeded, it would cause the republic to descend into violent upheaval. Being the pragmatic creatures that they are, this gives them pause.
If they wait until after the 2018 election, there won’t be enough GOPe left in the Senate to pull it off, in any case.