State and Local Tax (SALT) deduction cap is what he was referring to. The SALT cap hurt a lot of folks who were expecting to benefit from POTUS' tax bill.
'President Donald Trump said that New Yorkers could have thwarted a provision in his tax law that limits state and local tax deductions, one of the most controversial changes in the 2017 overhaul that contributed to Republican losses in the 2018 midterms.
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The $10,000 cap on state or local tax deductions, known as SALT, was one of the most fought-over provisions as Congress debated the law in 2017. The change, which mostly affects residents of high-tax Democratic states, led to a backlash from both Republicans and Democrats representing those states. The deduction was previously unlimited for some taxpayers.'
https://www.bloomberg.com/news/articles/2019-04-29/trump-new-york-tax-deductions