Avangrid executives once hoped to get state permits for their giant power line in western Maine by the end of the year. That turned out to be wishful thinking. Maine's Public Utilities Commission issued a new timeline Friday for its review of the 145-mile project, which would bring power from Hydro-Quebec's dams in Canada to Massachusetts. Now, the commission is shooting for March. This is just the latest delay. A separate review, by state environmental regulators, was already expected to spill well into 2019. The slowdown has emboldened opponents. This group includes unlikely allies: local power plant owners concerned about competition that's essentially subsidized by Massachusetts ratepayers, and environmentalists worried about the impact on woodlands and renewable energy sources. With each delay, the critics get more hopeful for a "Northern Pass scenario" — that is, death by regulatory scrutiny.