He's done better, but I agree. Not only will it further cement that he's a petty child, but it will further alienate the part of the right who wants actual effort of the presidency spent on leading the country and not pettiness. While most swing voters have already gone Democrat, just keeping more Republicans who come from the center of the party (and who don't care about trying to "trigger liberals) staying home will be good for 2018.
In that sense it probably will be the greatest thing he's done - to wreck his own presidency and party. So bring on the stupidity, I look forward to a Democrat majority in both houses come 2018, and full control come 2020 .