OKLAHOMA CITY (AP) — Oklahoma voters are deciding Tuesday whether to expand Medicaid to tens of thousands of low-income residents and become the first state to amend their Constitution to do so.

While an increasing number of Oklahoma voters took advantage of mail-in voting for Tuesday's primary, polls are open from 7 a.m. to 7 p.m. statewide.

Idaho, Maine, Nebraska and Utah have all expanded Medicaid through ballot questions, but did so by amending state statutes, according to the nonpartisan Kaiser Family Foundation.

Amending the Oklahoma Constitution will prevent the Republican-controlled Le...