Mitt Romney's presidential campaign said Friday it isn't worried about a series of national polls that shows the presumptive Republican nominee slipping significantly behind President Obama.

A senior adviser to Romney's campaign, briefing reporters in Boston about the candidate's upcoming bus tour, said Team Romney wasn't concerned about new surveys from CNN, Fox News and Reuters that show Romney between seven and nine points behind the president.

"It's the middle of summer, it’s the doldrums. It’s the Olympics. There has not been any national news that would push these numbers from -3 to -9," the adviser said, according to Buzzfeed.

The polls have shown significant movement for Obama among independents, while Romney's unfavorability rating has continued to climb. In the Fox News poll, more viewed Romney in a negative light than a positive one, while Obama had a net 14-point favorability advantage.

But the Romney aide said the polls were likely anomalies, and that recent campaign hiccups — like an international trip plagued by embarrassing moments — were not likely responsible.

"The impact of the European trip is negligible," the adviser said. "You’ve got to have something precipitate that sort of sea change, and we haven’t."