I think you nailed it right here.
This will be strike three, if it comes to pass. And no amount of hand-waving (eg, This is a tremendous bill or This is great for middle America or This is going to put more money in the pockets of working class Americans, believe me) by Trump will rescue 2018.
If the Senate version is what passes, forget about any gains in 2018, the miracle will be if the Rs dont lose any seats at all.
I think most could forgive a lot if the new tax law had just one thing (that the House version does have as far as I know now): saving the deductions for property taxes. If thats saved I think most will forgive that the mortgage interest deduction is going away. Or, if the standard deduction is increased even more.
If anyone from middle class sees even a penny of tax increase though for any reason its game over in 2018. Once again the Republicans try to find a way to snatch defeat from the jaws of victory.