Most important is that anyone can volunteer.

resident alien = non-immigrant alien/ permanent resident/ green card holder/ conditional resident/ returning resident

resident alien = non-immigrant alien/ permanent resident/ green card holder/ conditional resident/ returning resident non-resident alien = alien/ visa holder

A resident alien can contribute finanically to a campaign but not a non-resident alien. However, one can always volunteer.

No, one has to be either a US citizen or permanent resident to contribute to a campaign for federal office, and I encourage you not to look for ways to contribute indirectly. However, anyone can volunteer for a campaign.

No. There is a process by which candidates fill out questionnaires before SAFO decides to endorse someone, and that process moves along at a different pace for different campaigns for a variety of reasons. That is why the SAFO announcement says it is “SAFO’s Initial 2010 Endorsement Slate.”