Barack Obama and Hillary Clinton on Tuesday provided fresh evidence of their tendency towards mutual character assassination, with each trading allegations the other serially exaggerated or even fabricated episodes from their lives.
The Obama campaign seized upon Mrs Clinton's admission on Pittsburgh radio station on Tuesday morning that she "misspoke" last week when she claimed that she had been under threat of sniper fire on a visit to Bosnia as First Lady in 1996.
Mrs Clinton said she and her daughter, Chelsea, had run towards the vehicles with their heads down after their plane had made a "corkscrew" landing. She attributed her false claim, which was exposed on Monday with the release of footage by CBS, the network news channel, to the fatigue of a long and tiring campaign.
"I made a mistake – I'm human, which for some people is a revelation," she said. She added that it was the first time since her Bosnia trip that she had mischaracterized the visit. "I have written about it in my book and talked about it on many other occasions and last week, you know, for the first time in 12 or so years, I misspoke," she said.
The Obama campaign immediately emailed reporters with four recent instances where Mrs Clinton had aired a similar version of the retracted Bosnia story. That was followed by a Clinton campaign email citing ten recent instances in which Mr Obama had allegedly exaggerated his own record.
These included the claim that he had been a professor rather than a senior lecturer at Chicago University and instances where Mr Obama took credit for legislation that either was not enacted or with which he had little to do.
"Senator Obama's campaign is based on words –not a record of deeds – and if those words aren't backed up by facts, there's not much else left," said a Clinton spokesman.
Tuesday's exchange typified the increasingly settled pattern of a primary campaign that is barely halfway towards its conclusion in early June and which many Democrats fear could extend right up to the presidential convention in Denver in late August.
Owing to the slim likelihood Mrs Clinton will be able to eliminate Mr Obama's lead in the popular vote and among elected delegates by the end of the process and the fact there are few substantive policy differences between the two, many expect Mrs Clinton in particular to continue to hammer away at questions about Mr Obama's integrity.
The 795 superdelegates are thought very likely to endorse whichever candidate finishes ahead on the popular vote and among elected delegates unless there were to be some game-changing revelation that would invalidate the winner's electoral prospects.
Opinion polls indicate Mr Obama has been damaged but not fatally wounded by video footage of his former pastor, Jeremiah Wright, expressing anti-American sentiments. Mrs Clinton has a clear lead in Pennsylvania, which holds the next nominating contest on 22 April.