National City has asked former presidential candidate Bernie Sanders and his campaign to pay a $28,340 bill for the rally the candidate held there in May.

"We sent a demand letter today (Tuesday)," said Armando Vergara, the city's director of neighborhood services. "We've already sent the invoice four times.

About 7,000 people attended the May 21 rally in Kimball Park. The city was asked to put the event together 72 hours before it occurred.

"The Secret Service set requirements and we did our best to meet them," said Mayor Ron Morrison. "We had to cordon off 16 blocks, a four block by four block area around the park, provide security and get this set up in three days when we normally have months."

Vergara said they heard from the campaign once, via email. The campaign told them that the Secret Service was responsible for the biggest part of the cost: about $24,000 in police overtime for 30 National City officers and public works crews to set up and clean up after the event.

Calls to the Secret Service Monday and Tuesday were not returned.

"Usually you do these events at schools because they're surrounded by fences, have metal detectors and already have high security," Morrison said. "The park is this low point with seven-story buildings around it."

Morrison called the event a very positive one. "It was a very energetic crowd and they behaved really well," he said. "There were no incidents except for a couple of people feeling the effects of a very hot day." The Secret Service refused to allow water bottles inside the perimeter, Vergara said.

The Sanders campaign selected National City because of its demographics, Morrison said. "We're a working class and very diverse city," he said.

Everyone who attended went through metal detectors, and the TSA-like line extended from the park, down E. 12th to A Avenue, out to National City Boulevard and then up 16th, Vergara said.

"The last rally like this was when Bill Clinton came," he said.

The Secret Service sent an advance team that insisted on having the 16 blocks cordoned off, Vergara said.

Setting up included stages and tents for VIPs, working with the fire marshal to be sure there were break-away points so people could get out if something went wrong, and enough spots for emergency responders to get in.

"It was a nightmare for security," Vergara said. "But it went very smoothly. That's what was disappointing, we had the ability to make this possible with three days advance notice and then we didn't get paid for our costs."

The rest of the fees - after the $24,000, includes $1,366 for public works efforts to prepare the park and clean it up afterward, Vergara said. There was a $237 permit fee and $1,068.44 for blocking off streets, removing cars and setting up barricades. The fire inspector charged a $1,500 fee.

The city proclaimed Bernie Sanders Day and gave the senator a key to the city, Morrison said.