Election clerks check in voters for the primary election Tuesday in Lewiston. Robert F. Bukaty/Associated Press

For the first time in 20 years, Maine Democrats will head to the polls today for a presidential primary.

They’ll find a dozen contenders on the ballot, though only five of them are still active in what remains a hotly competitive race being played out across 14 states in a Super Tuesday showdown.

Maine’s primary marks a major departure from the caucus system used for the past four presidential election cycles and opens the door for many more Democrats to have a say in the outcome.

Republicans, too, have a primary but with only one name on the ballot – Donald Trump – the winner isn’t hard to predict.

In addition to the primaries, all Maine voters have the opportunity to cast a ballot in a referendum on vaccines.

Question 1 is an effort to repeal a new state law that requires students and health care workers to be fully immunized unless they have a medical exemption. A “yes” vote will repeal the law, while a no vote allows it to take effect.

The Democratic primary remains the focus of much attention following former Vice President Joe Biden’s big win in the South Carolina primary on Saturday that reshaped the race.

His unexpectedly large victory promoted two candidates to drop out – U.S. Sen. Amy Klobuchar of Minnesota and former South Bend, Indiana, Mayor Pete Buttigieg. They both endorsed Biden on Monday.

Election clerks Pauline Plourde, left, and Susan Gallant process absentee ballots for the primary election Tuesday. Robert F. Bukaty/Associated Press

Still in the race are Biden, former New York City Mayor Mike Bloomberg, U.S. Rep. Tulsi Gabbard of Hawaii and U.S. Sens. Bernie Sanders of Vermont and Elizabeth Warren of Massachusetts.

A third of the Democratic Party’s delegates – 1,344 in all — will be awarded during Tuesday’s primaries across the U.S. as well as a caucus in American Samoa.

With just 24 pledged delegates at stake, Maine hasn’t received much notice from candidates searching for bigger hauls in larger states, including primaries in California and Texas.

Each of the five remaining candidates, though, has been making some effort to round up votes in the Pine Tree State since every delegate may matter in the long run, especially given that some scenarios foresee a national convention whose outcome is not a given.

Democrats will choose nine delegates from the 1st Congressional District, seven from the 2nd Congressional District and eight more chosen statewide to attend the party convention in Milwaukee in July.

To get any of them, a candidate has to pull in at least 15% of the vote in either congressional district. Votes for contenders who fall short of the 15% mark are irrelevant when it comes to divvying up the delegates.

Election clerk Ginny MacDonald reinforces her instructions to a voter she checked in for the primary election Tuesday. Robert F. Bukaty/Associated Press

Democrats who voted early for a candidate who is no longer in the race are out of luck. There is no way to retract an early vote once it has been submitted.

The party’s shift from a caucus to a primary followed the request of both the Democratic National Committee and the Maine Democratic Party in a bid “to make it easier for eligible Mainers to participate in our democratic process,” Kathleen Marra, chairwoman of the Maine Democratic Party, said Monday

Marra said “with Donald Trump and Susan Collins on the ballot this year, the stakes for Mainers couldn’t be higher” so she is grateful “that our state leaders had the foresight to enact legislation that makes voting more accessible and convenient.”

Though the competitive presidential primary allows only Democrats to vote, Question 1 gives every Maine voter a chance to cast a ballot.

It also offers some suspense since its outcome is anything but certain.

Demi Kouzounas, chairwoman of the Maine GOP, who favors repeal of the measure approved by legislators last year, called it “a serious issue that requires us to look at how Maine balances the protection of the rights of Maine people versus any measurable benefit to public health.”

Opponents of the new law, like Kouzounas – who are looking for a yes vote – argue that parents ought to have the right to choose whether their children receive vaccines.

Further, they say it would force parents who oppose vaccination to pull their children out of public school and make some adults give up their health care jobs rather than accept vaccines they don’t want.

Supporters of the new law – who hope people will vote no – say that mandatory vaccines will help prevent potentially dangerous diseases and protect vulnerable Mainers who can’t be immunized for medical reasons.

Supporters, which include every major medical group in Maine, say immunizations save lives. The Maine chapter of the American Academy of Pediatrics, which is asking Mainers to vote no, said vaccines are “unique within the realm of medical intervention” because they protect not only the patient but also the community.

“Refusal of vaccination not only puts the individual child at risk, but also increases societal risk by decreasing community immunity and adding to a population of unimmunized individuals within which vaccine-preventable disease may spread,” it said.

Voters in Lewiston and Auburn can head to the polls from 7 a.m. to 8 p.m. Other locations begin later but all are open until 8 p.m.

All voting in Lewiston is taking place at Longley School while Auburn has polling locations in each of its five wards.

Follow this link to find polling locations in Androscoggin County. For polling locations in Franklin and Oxford counties, follow this link.