Hillary Clinton's campaign is "worried about" the challenge being posed by Sen. Bernie Sanders, whose popularity and poll numbers are continuing to grow, the former secretary of state's communications director acknowledged Monday."He's a force," Clinton campaign communications director Jennifer Palmieri told MSNBC's "Morning Joe" program. "He'll be a serious force for the campaign. We think that will — I don't think that will diminish."Clinton is often described as being the "presumptive nominee," said Palmieri, but "we don't normally say that, and the start will be really competitive."She acknowledged, though, that "it's to be expected that Sanders will do well in the Democratic primary" and in the Iowa caucuses.But still, she does not think the Clinton and Sanders campaigns need to attack each other."We all, you know, he'll run his campaign; we'll run ours," Palmieri said. "I think the imperatives for us are different. We think that what works for her particularly in Iowa is doing a lot of small events, staying for a long time, being one of the last people — if not the last person — to leave the room. ... That works better for us than doing big events."At the same time, Palmieri said, "of course we're worried" about Sanders."This is an election [and] he is doing well," she said. "And we'll have to, you know, we'll have to make our case. We knew this was going to happen."Palmieri on Monday also defended the campaign's decision on Saturday to have aides hold a rope tofrom the candidate during an Independence Day parade in New Hampshire.Palmieri said the action was taken to allow the residents in Gorham to see Clinton. The press, though, began tweeting photos of its colleagues being dragged back by the rope, adding to complaints that Clinton is intentionally keeping the media far away."We're talking about allowing as much access as possible," Palmieri said Monday, and that the press coming in too close at events "can get in the way of her being able to campaign."Clinton is having smaller events, she added, which are "really important to her," as she wants to be able to talk to voters.In other parades, press spots are pre-set at locations along the route, but this time, "we said, let it be open," and Palmieri, and while she was not at the event, she said she did see some press reports describing the scene as "chaotic," and the rope was put up "so the parade could continue and she could talk to voters."Reporter spots could have been "pre-set," said Palmieri, but "that is more restrictive." Further, she said, the campaign does not yet have all the vehicles available to allow reporters to follow along from the back of an open pickup truck.But the campaign's priority is to make sure Clinton can interact with voters, especially at the beginning of the race, as she was not able to talk with voters or campaign while she was secretary of state."You can't do that forever in a country of 300 million people," said Palmieri. "She really wanted to get that part done before we started talking about the national media, before we started doing big groups."Clinton "feels great" about the momentum of the campaign over the past few months, as she has been able to talk to voters, which has been difficult."The press is important," she said, laughing, when host Joe Scarborough jumped in to make that point. "But they're not as important as they think they are."