AUGUSTA — A bill to hold presidential primary elections in Maine took a step forward in the Legislature on Monday.

The Maine Senate voted 19-13 to give preliminary approval to a measure that would add Maine to the list of states that would participate in the “Super Tuesday” primary elections during the first week of March in 2020.

An amendment attached to the bill on Monday would allow each political party to decide whether to allow unenrolled voters to cast ballots in their respective primaries or to limit participation to registered members.

Maine is among the minority of states that hold presidential caucuses rather than primaries. Although the format varies from election to election, Maine caucus-goers typically gather in town halls, schools or other locations to hear speeches and then vote collectively for their presidential preferences. Caucuses usually take several hours but are valuable organizational and voter engagement events for the political parties.

The idea of switching to a primary system gained bipartisan traction after large crowds overwhelmed some caucus locations during the lively 2016 races for the Democratic and Republican nominations. In Portland, for instance, some Democrats waited up to four hours in line to get into the city’s caucus.

Lawmakers passed a bill in 2016 directing the Secretary of State to analyze the cost and logistics of holding primary elections instead of caucuses. This year, Secretary of State Matthew Dunlap’s office testified in support of the bill, L.D. 1626, to switch to presidential primaries.

But the issue has become more partisan since 2016, as evidenced by Monday’s divided vote. All 18 of the Democrats present on Monday voted in support of the bill but they were joined by only one Republican, Sen. Matthew Pouliot of Augusta.

The bill now goes to the Democratic-controlled House for consideration. A fiscal note attached to the bill estimates it would cost the Secretary of State’s office $122,000 to implement a primary election next year.