(CNN) Former Vice President Joe Biden is preparing for a lengthy Democratic primary battle despite his status as the front-runner in national polls, senior campaign aides said Tuesday.

Biden could withstand a loss in Iowa because of his strength among minority voters in the more diverse states that follow it in the presidential nominating process, the aides said.

"We expect this to be a fight. We expect this to go for a while," a senior campaign aide said during a call briefing reporters on Biden's approach to the campaign this fall.

"Do we think we have to win Iowa? No. Do we want to win Iowa? Yes, we do," the aide said. "We think we're going to win; we know it's going to be a dogfight. The same thing is true in New Hampshire."

The aide said Biden's campaign believes there will be "three or four" Democrats going deep into the race -- specifically pointing to Massachusetts Sen. Elizabeth Warren and Vermont Sen. Bernie Sanders as unlikely to depart early.