The popular provision may be on the tax reform chopping block for a simple reason: eliminating it would generate tens of billions of dollars in revenue needed to offset the money lost from lowering tax rates on individuals and corporations. For the tax years 2016 through 2020, letting taxpayers off the hook for taxes paid to state and local governments will cost the Treasury nearly $370 billion, according to a report from the congressional Joint Committee on Taxation.

Proponents of the provision have long argued that, without the provision, taxpayers would be hit twice for each dollar of income, once by their state and again by the U.S. Treasury. Opponents argue that the deduction benefits the richest taxpayers at the expense of those with lower incomes, or who don't own a home or make large purchases that carry a big sales tax.

One thing is clear: eliminating the deduction would hurt taxpayers who voted for Hillary Clinton a lot harder than it would those who voted for Donald Trump, according to a CNBC analysis of voter and tax data.