Both candidates intensified their attacks on the eve of the second of three presidential debates.

The debate (to be shown live on ABC1 at midday) will feature questions from an audience of undecided voters, a format preferred by Senator McCain, who frequently paces the stage and engages directly with voters, in contrast to Senator Obama, who tends to be more self-contained.

As polls continued to show Senator McCain sliding in the polls, the 72-year-old dug in his heels with repeated questions about Senator Obama's track record and a refrain by his running mate, Sarah Palin, that Senator Obama was ''palling around with terrorists''.

''What has this man ever actually accomplished in government?'' Senator McCain asked supporters on Monday.

''What does he plan for America? In short, who is the real Barack Obama? But my friends, you ask such questions, and all you get in response is another angry barrage of insults.''

Senator Obama's campaign countered that the Arizona senator was ignoring the world financial crisis and attempting to divert attention from shady economic dealings in his past, particularly a banking scandal more than 20 years ago.

The Illinois Democrat said, ''If John McCain wants to have a character debate, then I'm happy to have that debate because Mr McCain's record, despite him calling himself a maverick, actually shows that he is continually somebody who relies on lobbyists for big oil and big corporations.

''We don't throw the first punch, but we'll throw the last.''

Notwithstanding such rhetoric, the voter-question format could divert attempts to wage personal attacks during today's debate. The financial crisis remains a top concern after stocks plunged despite President George W.Bush's signing of a $US700 billion rescue package last Friday.