Electioneering missteps in Denver Public Schools in the race for the U.S. Senate sent one principal to the woodshed and have Sen. Michael Bennet's campaign offering up a mea culpa.

Bennet's campaign recently sent mailings to at least one school seeking the principal's support. And a flier for a Bennet fundraiser was handed out by one principal to others at a district workshop — both inappropriate campaign actions, Bennet's campaign acknowledges.

"If anything happened at work, it's a mistake and we would do anything possible to prevent that from happening again, and it shouldn't have happened in the first place," said Bennet's campaign manager, Craig Hughes.

School-board member Jeannie Kap lan, a supporter of Bennet's Democratic rival in the primary, Andrew Romanoff, said the actions are causing unease among some principals.

"They feel afraid," said Kaplan, who is running unopposed to retain her school-board seat. "I don't want our principals to be under that pressure — to support a particular political agenda."

Bennet was Denver's superintendent for more than three years, resigning in January after Gov. Bill Ritter picked him for the U.S. Senate.

Bennet's longtime friend and former prep-school classmate Tom Boasberg was unanimously approved by the school board to be the district's current superintendent.

Principals, who serve at will under the superintendent, refused to speak on the record about whether they are feeling pressure.

Romanoff's campaign issued a statement Thursday.

"This election is about allowing individuals to decide who they think will best serve Colorado and to exercise their own judgment free from any kind of pressure," said Joelle Martinez, spokeswoman for Romanoff for Colorado.

Last month, Bennet's campaign sent a letter from former Colorado Gov. Roy Romer to 40,000 recipients across the state, urging them to support the junior senator.

At least one of those mailings was sent to a principal at a Denver school address.