An Alabama legislator aims to put a “fair tax” proposal on the 2020 ballot, predicting that high turnout in “a very red state” would give the conservative tax overhaul its best shot at success.

But first, Rep. Mike Holmes (R) will have to win over his fellow state lawmakers.

His plan would end the state’s income, sales, and use taxes and replace them with a flat-rate consumption tax on goods and services of just over 8%, said Holmes, sponsor of the legislation. It comes in two parts: a proposed constitutional amendment via H.B. 3 and implementing legislation via H.B. 4...