The Maine Green Party is ballot-qualified, and must nominate all its candidates in its own primary. It is so difficult for small qualified parties in Maine to get candidates on their own party’s primary ballot, the Green Party has never been able to get anyone on the ballot for either house of congress, in years when it was qualified. However, in 2020, David Gibson will try to run for U.S. Senate. See this story.
The Maine 2020 U.S. Senate election will use ranked choice voting. It will be the first ranked choice voting in a U.S. Senate race, anywhere in the nation. Although Maine had ranked choice voting for congressional elections in 2018, there was no U.S. Senate race up in 2018 in Maine.