US:BARACK OBAMA and Hillary Clinton face off in Mississippi today as the two candidates continue to bicker over foreign policy qualifications and which of them is ready to be commander in chief.
As the Clinton campaign repeated yesterday that Mr Obama had not passed "the commander-in-chief test", Mr Obama ridiculed Mrs Clinton's suggestion that he could serve as her vice-president.
"With all due respect, I've won twice as many states as Senator Clinton. I've won more of the popular vote than Senator Clinton. I have more delegates than Senator Clinton," Mr Obama told a meeting in Columbus, Mississippi.
"So I don't know how somebody who is in second place is offering the vice-presidency to the person who is in first place. I was just wondering, because if I were in second place I could understand it. But I'm in first place right now."
Mr Obama noted that the Clinton campaign had spent the past two or three weeks arguing that he was not ready to be president but were now talking about him as a possible vice-president.
"I don't understand. If I am not ready, why do you think I would be such a great vice-president?" Mr Obama said to a standing ovation.
"You can't say he is not ready on day one, then you want him to be your vice-president. I just want everybody to be absolutely clear: I am not running for vice-president. I am running to be president of the United States of America."
Mrs Clinton's spokesman, Howard Wolfson, said that, although Mr Obama was not ready to be commander in chief now, he could be ready in time for the Democratic national convention in Denver next August.
"We do not believe that Senator Obama has passed the commander-in-chief test. But there is a long way between now and Denver," Mr Wolfson said.
Polls predict that Mr Obama will win today's primary by a wide margin and Mrs Clinton was already campaigning in Pennsylvania, the next state to vote on April 22nd.
Mr Obama enjoys a comfortable lead among the delegates who will choose the Democratic presidential nominee and only a series of landslide victories would enable Mrs Clinton to catch up. Mr Obama has also seen a number of superdelegates - elected officials and senior party figures who account for a fifth of the nominating votes - endorse him in recent days, although most uncommitted superdelegates are holding back for the moment.
Mrs Clinton is hoping that a convincing victory in Pennsylvania will help to sway superdelegates that after winning almost all the big states, she is best placed to defeat John McCain in the battleground states next November.
Winning Pennsylvania would also help Mrs Clinton to close a gap of 600,000 with Mr Obama in the national popular vote. If votes cast in unauthorised primaries in Michigan and Florida are counted, the gap in the vote disappears.
The Clinton campaign believes that attacking Mr Obama helped Mrs Clinton win key victories in Texas and Ohio last week and she plans to keep up the pressure on him in the six-week run-up to Pennsylvania's primary.
Mississippi Republicans also vote today, although their primary has little significance now that Mr McCain has enough delegates to secure the nomination. He is spending this week fundraising across the US and he will travel next week to the Middle East.