A series of top staff members have resigned from the Herman Cain campaign over the past week, but the Republican presidential candidate is downplaying the significance of their departures.

"We have a staff of nearly 35 permanent people and thousands of volunteers in Iowa; this is not a big deal," Cain said on Fox News.

Cain told Fox' Chris Cotter that the process of finding replacements had already started before Iowa state director Tina Goff and Iowa straw poll coordinator Kevin Hall submitted their resignation from the campaign. Charlie Gruschow, founder of the Des Moines tea party, also resigned over the weekend.

"It wasn't like we didn't expect something like this to happen," Cain said. "We were not caught off guard. We have lost absolutely no momentum."

Today, the Cain campaign announced it had hired four new Iowa staffers: Larry Tuel as the new state director and Lisa Lockwood, Zach Dalluge and Steven Hensler as field staff.

The turnover in Iowa comes soon after the loss of key New Hampshire leadership. Early last week, Cain's New Hampshire campaign director Matt Murphy and regional director Jim Zeiler also resigned. Cain spokesperson Ellen Carmichael says more hires, including the name of a New Hampshire state director, will be announced at the end of this week.

The departures of Cain's Iowa and New Hampshire directors coincided with criticism that the candidate has not launched a serious organizing effort in the early primary states.

To these critics, Cain said, "There is only one Herman Cain and I cannot be everywhere everybody wants me to be," noting that his most recent trip to Iowa on Sunday was his "22nd trip since the beginning of the year" and that he's committed to participating in the Ames Straw Poll.

"My commitment to Iowa, Chris, cannot be denied if you look at the facts," Cain said.