At some point, if you go to far with it, everything is bribery.  What's a campaign promise, or friendly free soda for delegates who stop by a booth, if not a quid pro quo?

No, I maintain that bribery, spirit and letter, is a high crime or misdemeanor.  It must involve significant sums of exchange to a very concentrated and powerful interest -- institutional officials, not voter or delegates.  Promises or minor gifts to diffuse interests like the grassroots delegates to a democratic body, are just being creative and friendly -- no different than a warm two-handed handshake and smile.