An uninvited guest turned up Tuesday morning at the Port Chester Nursing Home in Westchester, where Harold Ford Jr. was paying a visit. “He was really young, about 20, and he had a flip camera,” said an aide to the potential challenger of Sen. Kirsten Gillibrand. “I asked him where he was from, and he said he was working for Gillibrand.” The “tracker,” as such operatives are known on the campaign trail, was shown the door but was later spotted getting into the car of Daily News reporter Dave Saltonstall, one of Ford’s harshest critics. Ford’s rep, Tammy Sun, said, “It’s unethical at best.” Neither The Daily News nor Saltonstall returned calls.