Barack Obama poured scorn yesterday on suggestions that he will be Hillary Clinton’s Democratic vice-presidential running-mate, pointing out that it was he – not she – who occupied pole position in the race for the nomination.

He also sought to turn the idea of a joint ticket, which has been raised repeatedly by the Clintons in recent days, into a shield against attacks that he is not ready to be commander-in-chief of the US military.

In a speech in Mississippi, where he expects to win today’s primary, he said: “With all respect, I won twice as many states as Senator Clinton, I won more of the popular vote than Senator Clinton, I won more delegates than Senator Clinton. So I do not know how someone who is in second place is offering the vice-presidency to someone who is in first place.”

Nor, Mr Obama added, did he understand “how it is if I’m not ready, how you think I can be such a great vice-president?”

Howard Wolfson, Mrs Clinton’s spokesman, provided an answer to that last question even before Mr Obama rose to speak: “We have said that Senator Obama has not passed the commander-in-chief test. This is an issue that voters and reporters are asking [him] about.”

He went on to add that it was a “long time between now and Denver” – where the nominating convention will be held in August – “and this is something she will not rule out”. He declined to elaborate on what Mr Obama can do between now and August to pass the test.

There has been growing irritation inside Mr Obama’s campaign over repeated suggestions since Mrs Clinton’s comeback victories in Texas and Ohio last week that he could form the junior half of a presidential ticket.

Bill Clinton, speaking in Mississippi at the weekend, claimed that such a team – topped by his wife – could become an “unstoppable force”. The message appears to be aimed at voters who are enthused by the prospect of an African-American president but harbour doubts about Mr Obama’s relative inexperience – as well as the elite group of “super-delegates” who appear likely to decide the outcome of the race.

The Clinton campaign still hopes to ensure that votes from Florida and Michigan will count at the convention, even though delegates are currently banned because of a party rules dispute.

Yesterday it emerged that two of her most most powerful supporters, Jon Corzine and Ed Rendell, the governors of New Jersey and Pennsylvania, were offering to raise $15 million (£7.5 million) to help to pay for new primaries that could help to close the delegate gap or even overtake Mr Obama in the popular vote. Yesterday Mr Obama stopped short of explicitly ruling out being on a joint ticket but told his rally: “I don’t want anyone thinking we can get both.” He threw back at Mr Clinton remarks he had made in 1992 stating that a vice-president must be ready to step into the breach as commander-in-chief.

“They’re trying to bamboozle you. They’re trying to hoodwink you. You cannot say I’m not ready on Day 1 unless I’m ready to be vice-president and then I’m ready on Day 1,” Mr Obama said to laughter.

Both campaigns rolled out an array of retired military leaders yesterday to vouch for their candidates’ national security credentials.

General Wesley Clark, who has endorsed Mrs Clinton, contrasted her “strength and resolution” with remarks made by Mr Obama’s former foreign policy adviser that suggested that he would not be bound by any promises to withdraw troops from Iraq.

Lieutenant-General Joe Ballard used an unusual metaphor to explain his support for Mrs Clinton, saying: “I grew up in Louisiana and learnt a lot about milking a cow. Just because you recognise a cow doesn’t mean you know how to milk it – you need a broad body of experience to do it.”

Richard Danzig, the former Navy Secretary, who is backing Mr Obama, said that his initial scepticism about the candidate’s experience had been replaced by an admiration for character, judgment and vision, adding: “He would make an extraordinary commander-in-chief.” Mr Obama also hit back yesterday at Mrs Clinton’s “3am” advertisement, which suggests that she would be better placed to answer a crisis telephone call in the White House, as he once again pointed out her early support for the Iraq war.

“I am not running for vice-president, I’m running for President of the United States of America, I’m running to be commander-in-chief,” he said. “The reason I’m running to be commander-in-chief is because I believe that the most important thing when you answer that phone call at 3am is what kind of judgment you have.”

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