That massive number is the reduction in home values caused by the 2017 tax law that capped federal deductions for state and local real estate and income taxes at $10,000 a year and also eliminated some mortgage interest deductions. The impact varies widely across different areas. Counties with high home prices and high real estate taxes and where homeowners have big mortgages are suffering the biggest hit, as you’d expect, given the larger value of the lost tax deductions. But as we’ll see, homeowners living in blue states all over the country are feeling the effects.