Barack Obama shares a joke with his supporters at a campaign stop at Jackson State University in Jackson, Mississippi. Photograph: Alex Brandon/AP

Mississippi voters go to the polls this morning after confirmation from the Democratic presidential candidate Barack Obama that he would not accept any prospective down-ticket offer from his rival, Hillary Clinton.

At a rally in Columbus, Mississippi, last night, Obama drew cheers from the 1,700-strong crowd when he scoffed at Clinton's hint that she would offer him the vice-presidential job. Clinton's team had suggested a Clinton-Obama ticket would be popular, and formidable, against the Republican nominee, Senator John McCain, in November.

"I don't know how somebody who is in second place is offering the vice-presidency to someone who is first place," Obama said.

"I don't want anybody here thinking that 'Somehow, maybe I can get both'," by nominating Clinton as president and assuming he would be her running mate, he said. "You have to make a choice in this election."

Obama reiterated the sentiment in a later interview, saying he would "absolutely close out any possibility" of taking the ticket's second spot. "I am not running for vice-president, and don't intend to be the vice-president."

Obama is hoping to increase his delegate count lead in the Democratic contest with a second-straight primary victory today.

Mississippi, which will award 33 delegates based on today's vote, is predicted to go Obama's way. The Illinois senator has won every southern state, except his rival Hillary Clinton's former home, Arkansas, where her husband, Bill, was governor. More than half of Mississippi Democratic voters are black, a voting bloc which has carried Obama to victory in other states.

Obama's camp rides into Mississippi with some momentum after Saturday's victory in the Wyoming caucuses. His win there reinvigorated his campaign after Clinton put the brakes on his nomination drive with crucial wins in the mega-states of Ohio and Texas, and a further victory in Rhode Island, last week.

Obama is ahead in the overall delegate count, with 1,578 compared to Clinton's 1,472, according to an Associated Press tally. With 2,025 needed to clinch the nomination, neither candidate will be able to reach that number without the votes of about 800 superdelegates - Democratic party insiders and elected officials who are not bound to the results of the state votes. Obama and Clinton have been courting superdelegates aggressively.

Last night, Obama's campaign moved to counter Clinton's allegations that their candidate is unqualified to be commander-in-chief of the armed forces by rolling out three former military chiefs.

The former secretaries of the army, navy and air force said Obama's judgment, temperament and ability to inspire were more important factors than a lack of executive experience, which he shares with Clinton and Republican nominee John McCain.

The secretaries, who worked in past Democratic administrations, including that of Clinton's husband, also said Obama's ability to manage an effective presidential campaign confirmed his administrative prowess.

"If the phone rings in the White House in the middle of the night, the thing you most need is a plan, a policy and an organisation that can actually do something," said F Whitten Peters, secretary of the air force under President Bill Clinton, "otherwise why get up."

Peters said Obama's ability to draw young voters would aid military recruitment efforts, because he would inspire youngsters to serve their country.

Clifford Alexander, secretary of the army under President Jimmy Carter, dismissed Clinton's touting of her relationships with military brass and foreign leaders as inconsequential.

"It's important not to count the number of countries you've gone into, not to count the number of people that you know, but to understand fully that you are going to be a better leader if you have consistency, good judgement thoughtfulness and an ability to execute," he said.

President Clinton's navy secretary, Richard Danzig, spoke of Obama's "freshness of vision", which he said would restore America's standing in the world. Danzig spoke against what he described as McCain's "militarisation of national security".

The three secretaries spoke after a rough period for Obama's campaign that saw Clinton leap on comments made by two foreign policy advisors. Austan Goolsbee, a University of Chicago professor, recently appeared to indicate in a meeting with Canadian officials they should take Obama's political pronouncement on the North American Free Trade Agreement with a grain of salt.

Last week, one of his foreign policy advisors, Samantha Power, was forced to resign after referring to Clinton as a "monster". She also said Obama's ultimate Iraq policy may differ from what he proposes on the campaign trail. The Clinton campaign sought to use her statements as evidence that Obama was not being candid with voters.

The Clinton campaign remained on the foreign policy offensive yesterday, holding a conference call with reporters to attack Obama's Senate record on Iraq.

Retired general Joe Ballard, who has endorsed Clinton, reiterated the position that experience is more important than "a great speech" and "a great staff", comparing running the military to milking a cow.

"When you look at what Senator Obama would bring to the table, there's no doubt in my mind that he probably can recognise a cow, but his body of experience doesn't necessarily make him an expert on how to milk one," he said.

Lee Feinstein, a foreign policy advisor to Clinton, accused Obama of populist policy-picking: "[He] didn't introduce a plan to withdraw from Iraq until he started running for president. He didn't oppose funding the war until he started running for president."

Source: http://www.guardian.co.uk