Me. Rev. Stat. tit. 21-A, § 353

A person who seeks nomination by petition qualifies by filing a nomination petition and consent as provided in sections 354 and 355. If enrolled, the person must also withdraw enrollment in a party on or before March 1st to be eligible to file a petition as a candidate in that election year, as provided in section 145. The registrar in the candidate's municipality of residence must certify to that fact on a form designed by the Secretary of State.