You still haven't figured President Trump out? Even more important than his promise to build a wall was his promise to only nominate Conservative Constitutional originalists. There is no way that the President would ever go back on that promise.
The SCOTUS nomination is forever; the fight over the wall will still be there next week, and the week after that...
Besides, Democrats never negotiate in good faith; they will take the nomination and then renege on the wall funding.
-PJ