Who the fuck says it has to be a Democrat?

Platner won the Democratic primary, so the Democratic Party of Maine will select the winner according to Maine law and the state Democratic Party charter. From the Portland Press-Herald article I linked above:

According to Maine law, if a candidate nominated in a primary election withdraws on or before 5 p.m. on the second Monday in July — July 13 this year — a replacement candidate can be named. Platner dropping out now makes that replacement process possible.

The Democrats have until the fourth Monday in July — July 27 this year — to fill the vacancy, according to the Maine Department of the Secretary of State.

According to the Democratic Party charter, the process for naming replacement candidates includes convening a nominating meeting assembled by a person appointed by the party chair.

The charter does not provide great detail on the process for picking a replacement but says the meeting should be run in accordance with state law and the party charter.

This is an archive link to the above Press-Herald article; I am aware there are problems with the archive site but it has the content. Use at your own discretion: https://archive.md/FaCOR