BRUNSWICK, Me. — Angus King is the prohibitive favorite to win the open Senate seat in Maine this year, and it is easy to see why.

At a town-hall-style meeting to discuss technology issues here the other day, he showed a smooth rapport with the audience. They seemed impressed by his knowledge, chuckled at his dry wit and generally bathed in the warm glow of familiarity as he made casual references to his family and his two terms as governor.

This is the calm before the storm.

“A huge negative campaign is about to start,” said Juliana L’Heureux, 66, a politically active nurse who came here to see Mr. King and who likes him so much that she held a fund-raiser for him at her home. “Thank God he has a huge reservoir of good will, because he’s going to have to draw that down as things get nastier.”