WASHINGTON, D.C. — Headed for a final vote this week to be on President Donald Trump’s desk by Christmas, the “Tax Cut and Jobs Act” is the largest one-time reduction in the corporate tax rate in American history and lowers taxes for the vast majority of Americans and small business owners — at least until those cuts expire after eight years.Last-minute changes to the GOP’s plan give a larger break to the wealthy and preserve certain tax savings for the middle class, including the student loan interest deduction, the deduction for excessive medical expenses and the tax break for graduate students.