Eisenberg is a well-known locally with a history of mental-health problems, who told his son to "watch the news today."
Chelsea Coull, an employee at the town's Governor's Inn, told WMUR-TV that a young man identifying himself as Eisenberg's stepson told her that his father had been drinking heavily for 72 hours, and hadn't been in a right state of mind for three months.
Coull also said the stepson told her his father had asked where to buy roadside flares.
Witnesses at the scene said a women and her baby ran from the building and called police at around 1 p.m.
"A young woman with a 6-month or 8-month-old infant came rushing into the store just in tears, and she said, 'You need to call 911. A man has just walked into the Clinton office, opened his coat and showed us a bomb strapped to his chest with duct tape,'" witness Lettie Tzizik told WMUR-TV.
"This is a very serious ongoing situation. Law enforcement officials are coordinating closely and we are all hopeful for a quick, safe resolution," New Hampshire Gov. John Lynch said before Eisenberg was apprehended.
The Rochester offices of Clinton's Democratic presidential contenders John Edwards and Sen. Barack Obama were closed and evacuated, and a local school was on lockdown.
Clinton's campaign offices in Iowa were also shut down.
The Associated Press contributed to this report.