Ben Carson in Columbia, South Carolina, January 9, 2016. Photo: Reuters/Randall Hill

Carson was once seen as a formidable foe to frontrunner Donald Trump. But after questions began to swirl about the veracity of his autobiography, the retired neurosurgeon watched his poll numbers tumble.

The spiral was made worse when campaign manager Barry Bennett and spokesman Doug Watts announced they were leaving the campaign, citing differences with another top advisor, Armstrong Williams.

Carson is also facing staffing problems at the Super PAC that is backing his campaign. All five paid pro-Carson Super PAC staffers in New Hampshire defected to Ted Cruz, the New Hampshire news channel WMUR reported on Monday morning.

After the December departures, Carson named Ed Brookover his new campaign manager.

On Monday, Carson added A. Larry Ross to lead his communications team.

“We are in a battle for the soul of our nation, and I am motivated by Dr. Carson’s vision and passion to equip and empower each individual to move out of a culture of entitlement and dependency by taking responsibility and seizing opportunities, as each individual does his or her part to renew America,” Ross said in statement announcing the changes.

Carson added Christopher Bourne, a retired colonel in the Marines, to serve as the head of his policy staff.

Additionally, Jason Osborne, who was already working for Carson, was promoted to work on the communication team after previously serving as a deputy senior strategist.