Milk is allowed due to a 1966 Senate precedent stating that "there is nothing in the rules to prohibit the senator from requesting a glass of milk."

Republican Sen. Bill Cassidy of Louisiana, who is also a gastroenterologist, told CNN it is meant to help senators with peptic ulcers.

"There was no medicine for peptic ulcer disease so people would drink milk, and so the senators were allowed to drink milk because they had ulcers," he told CNN.

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The impeachment trial has strict rules on what food and drinks senators can consume in the chamber. The only drinks allowed are still or sparkling water and milk.

While milk may seem like a strange exception to the rule, Republican Sen. Bill Cassidy of Louisiana, who is also a gastroenterologist, told CNN that it is meant to help senators with peptic ulcers.

"There was no medicine for peptic ulcer disease so people would drink milk, and so the senators were allowed to drink milk because they had ulcers," he told CNN.

A Senate precedent was set in the 1960s allowing the dairy product on the Senate floor.

"There is nothing in the rules to prohibit the senator from requesting a glass of milk," the 1966 precedent reads.

While no outside foods and drinks are allowed in the Senate Chamber, some senators have been breaking the rules by bringing beef jerky and candy to their desks.

Cassidy told CNN that senators are offered snacks and coffee in the Senate cloakroom, but joked that the coffee wasn't very good quality.

"It's miserable coffee," Cassidy told CNN. "You would wish it on a Democrat but no one else."

"Just joking," he said.

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