I have not read about it anywhere so I hope my math is wrong, but here is how I calculated it:
In 2017: Gross income $500,000, state tax at 9%, IRS marginal tax rate 39.5%.
Net state tax after IRS deduction = ( $500,000 * 9%) * ( 1 - 39.5%) = $27,225
In 2018: Gross income $500,000, state tax...