Me. Rev. Stat. tit. 21-A, § 339

The primary election shall be held on the 2nd Tuesday of June of each general election year and is considered to be a separate election for each party which takes part in it. This includes the duties of public officials in announcing the election, providing forms and ballots, keeping records and any other matter necessary to effect the purpose of a primary election. A primary election shall be conducted the same as the general election, as nearly as practicable, for each party.