FRAMINGHAM – Elizabeth Warren peered over the edge of a trench where workers were lowering a sewer line into the mud and listened intently as a man in a hard hat extolled the sweeping benefits of better plumbing promised by the $22 million project.

A day later, Senator Scott Brown showed up just 3 miles away, donned his own hard hat — labeled “Senator Brown” — and handed doughnuts and coffee to workers installing drywall in a partially constructed Framingham bank.