The camp of Hillary Clinton is not going easy on her campaign strategy even though she is leading other Democrat presidential hopefuls by more than 40 points in a CNN national poll released on July 1, her top aides revealed.

Jennifer Palmieri, the communications director for Clinton's campaign, admitted that they are worried about a "serious force" among the contenders in the Democratic presidential nomination who could stand in their way to the White House.

Palmieri insisted that Vermont Senator Bernie Sanders could overtake the former US Secretary of State in Iowa polls by fall with the huge crowd he has been gathering in the Hawkeye state, posing a real threat in the first Democratic primary state there.

"We are worried about him, sure. He will be a serious force for the campaign, and I don't think that will diminish," Palmieri said in an interview for "Morning Joe" that was aired on MSNBC on Monday, according to The Hill.

"It's to be expected that Sanders would do well in a Democratic primary, and he's going to do well in Iowa in the Democratic caucus," she noted.

Last week, a new Quinnipiac University poll revealed that Sanders doubled his share of Democratic supporters in Iowa in just seven weeks.

Clinton's campaign manager Robby Mook acknowledged that Sanders could emerge as Clinton's main foil in the first nominating contest in Iowa.

"We take nothing for granted in Iowa because the caucuses are always such a tough proving ground," Mook explained, according to the Business Insider.

An unnamed official also admitted that Clinton's team "underestimated" the political strength of the independent senator from Vermont in attracting many Democrats in Iowa who may not like to bet on the wife of former President Bill Clinton.

"It's too early to change strategy because no one knows if Sanders will be able to hold on to these voters in the months ahead. We're working hard to win them over, but yeah, it's a real competition there," one of Clinton's advisers said, according to the New York Times.

This, Palmieri explained, has prompted them to lower their expectation in the early-voting states.

"Every candidate wants to be able to claim momentum — regardless of what actually happens. And Clinton has long sought to avoid looking like she's taking her party's nomination for granted," Palmieri said, according to the Business Insider.

But the advisers for the Vermont senator do not agree, dismissing any notion from Clinton's campaign team that "she was anything but the clear frontrunner in Iowa."

"That's just political chatter and usual tactics. What's important is what we saw at Bernie's recent event in Wisconsin—a candidate speaking to the issues facing Americans and 10,000 people coming out for it," Sanders' campaign manager Jeff Weaver said, according to the New York Times.

While Sanders continues to gather ample crowds by offering ambitious proposals to major problems in education and jobs, Clinton's name keeps on popping up to lead all GOP candidates in head-to-head general election match-ups.

In a national poll released on July 1, CNN revealed that Clinton has been leading all other candidates with 57 percent of Democrats and Democratic-leaning independents behind her.

Trailing behind her are Vice President Joe Biden, who earned 16 percent backing, and Sanders with 14 percent support.

"The poll holds better news for Biden than it does for Sanders, who has made gains against Clinton in recent polling in Iowa and New Hampshire. But Biden actually tops the list as national Democrats' second-choice candidate, 35 percent say he's their second pick, compared with 14 percent who say Sanders is," CNN Polls said.

"While both trail Clinton by wide margins on all four candidate attributes tested, Biden tops Sanders on three of them: as the strongest leader in the field, having the best chance to win, and representing the values of Democrats "like yourself," it added.