PORTLAND — Graham Platner couldn’t be found at the Maine Democratic State Convention until minutes before his speech Saturday evening. It had been three days since the Sullivan oyster farmer became the party’s presumptive nominee to challenge five-term Republican incumbent Sen. Susan Collins this fall. Yet though he wasn’t there in person for most of the day, his aura loomed large. Platner buttons were ubiquitous. Attendees described their feelings on the convention and their feelings on Platner often as one and the same — excited. Oliver McAvoy of Limington at the Maine Democratic Convention in Portland Saturday. (Shawn Patrick Ouellette/Staff Photographer)...