1: https://irc.bloombergtax.com/public/uscode/doc/irc/section_1...
Same thing happened when they restructured tax code to interpret withholdings differently. Everyone saw more on their paycheck temporarily (and they gave speeches about it!) but owed more later if they didn't change their withholdings.
So it’s likely the second — and was likely used in part to pay for those very same withholding changes! Or the then-new tax-exemption for lobbying expenses.