First, you need to understand the difference between an endorsement and a nomination. In the simplest terms, the difference is that a nomination is determined by state statute and procedures, while an endorsement is controlled solely by our party bylaws and procedures. More importantly, a nomination affects how party labels will appear next to a candidate's name on the General Election ballot, but an endorsement will not.
The standard and most straightforward way to be nominated by the Party is to win the Progressive Primary, either as a write-in or as a listed candidate. As a write-in, a candidate must get more votes than a listed candidate, OR, if there are no other listed candidates, get at least half as many votes as they would have needed signatures to get on the Primary ballot. For example, a candidate for State Representative needs 50 signatures to get on the primary ballot, so they would need 25 votes to win the primary as a write-in.
The other way to get the Party's nomination is to have a district committee fill an “anticipated vacancy” by holding a meeting by the filing deadline for the Primary (June 12th this year). The odd thing about this is it has to be done before we even know for sure who will be running in our primary. It's also a little confusing on the Senate and House level, as the District Committee isn't necessarily the same as a Town or County Committee. Burlington, for example, is divided into several House Districts, while other House Districts are made up of multiple towns. And Senate Districts do not correspond exactly with counties (so a Chittenden County Committee member from Colchester would not be a part of the Chittenden Senate District Committee, as Colchester is part of the Chittenden-Grand Isle Senate District).
District Committee meetings must be warned in writing to all members in the district at least 5 days before the meeting. At the meeting, the District Committee must elect officers (as with Town Organizing) and then can fill anticipated vacancies. On the state level, the Party's State Committee will address “anticipated vacancies” at our meeting on May 31st. It's important to remember that no matter who a Committee nominates (or endorses), the results of the primary take precedence. But although who we endorse (or choose not to endorse) has no binding control over who can run as a Progressive, it allows a party to publicly show support or lack of support for a particular candidate.
By our bylaws, endorsements are controlled by the appropriate Party Committee (Town, County, or State); there's nothing about “district committees.” At our May 31st meeting, it's likely that the State Committee will endorse all the candidates that it nominates to fill “anticipated vacancies” in the statewide slate. However, it should be noted that there is nothing that says they have to, or that they must only endorse one candidate for each office.