The Colorado Democrat's campaign said the 22-year-old intern was let go after it learned of the incident, which was first reported by The Wall Street Journal.
Campaign spokesman Trevor Kincaid said the intern took it upon himself "to cross a very serious line" not practiced or supported by the campaign, which has intricate protocols for interns.
"While extensive support from eager volunteers are the backbone of successful campaigns, it's not always easy to instill the importance of following the letter of a campaign's rules and philosophy," Kincaid said.
Bennet was appointed last year to the U.S. Senate to replace Ken Salazar, now Interior Secretary. Bennet faces former state House Speaker Andrew Romanoff in the Aug. 10 primary.
The intern, Jeffrey Garofano, a student at Middlebury College in Vermont, didn't respond to an email from The Associated Press seeking comment. He began working for the campaign June 1.
An e-mail sent from Garofano's personal account told a person asking about upcoming campaign events and a chance to pitch a bill on fuel standards to Bennet that an hourlong meeting with the candidate could be set up for $2,400.
Hosting an event for $5,000 or more would be a better chance to lobby him, according to the email.
The e-mail also said the congressional staff, rather than the campaign staff, might have better information on Bennet's stance on the legislation.
Kincaid said Bennet is "completely accessible" and stays late to talk to people on the campaign trail.
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