Robert F. Kennedy Jr. showed up too late to testify Tuesday in a court case in Pennsylvania where Democratic activists are trying to bar him from the ballot for president in the premier battleground state, prompting testy exchanges between the judge and Kennedy's lawyer.

Lawyers for the two Democratic activists who filed the challenge say Kennedy's candidacy paperwork states a fake home address—an allegation being aired in other state courts—and falls short of the signature-gathering requirement applied by state law to third-party candidates.