Barack Obama has forcefully rejected Hillary Clinton's suggestion that they would make a Democrat dream ticket for the White House if he was her vice-presidential running mate.
It was, he said, a brazen attempt to "okeydoke, bamboozle and hoodwink" his supporters. "I am not running for vice-president," he told an enthusiastic audience of mostly black students at Mississippi University for Women. He denounced Mrs Clinton's offer as another example of "Washington double-speak".
How could it be, Mr Obama asked, that he could be such a great vice-president when Mrs Clinton was saying he was not up to the job of commander in chief? "You cannot say [I'm] not ready one day and the next say [I'm] ready to be vice-president," he said.
In the race for the White House, Mrs Clinton's Achilles' heel is the level of distrust she generates among some voters. By going on the offensive and describing her as yet another duplicitous Washington-style politician, Mr Obama was putting down a marker that he believes she cannot win a presidential election.
"With all due respect, I have won twice as many states as Senator Clinton, more of the popular vote and I have more delegates," he said. "So I don't know how somebody who is in second place can offer the vice-presidency to somebody in first place." The latest poll shows Mr Obama leads his rival by 58 per cent to 34 per cent in Mississippi. He is also still leading in the national polls.
His victory in Mississippi seems assured, but in this racially polarised state Mrs Clinton still leads by 13 points among mostly white independents and Republicans who can vote in the primary. Mrs Clinton is focusing her energies instead on the delegate-rich Pennsylvania race – which votes on 22 April – where she is expected to do well.
Neither Mrs Clinton nor former president Bill Clinton have bothered to campaign in the state since she floated her running mate suggestion last week. That Mr Obama took so much time on the issue in his speech yesterday, suggests that his campaign is worried that Mrs Clinton has continued to dominate the airwaves and the news agenda since her big wins in Ohio and Texas last week.
He pointed out that in 1992 President Bill Clinton said that the most important criterion in selecting a vice-president was his or her readiness to step into the role of commander in chief at a moment's notice.
Despite a convincing win in Wyoming over the weekend, and the optimism about Mississippi, Mr Obama is still being outmanoeuvred by his rival. By going on the offensive, she has dominated the airwaves and turned her victories in Ohio and Texas into a test of Mr Obama's electability.
According to the Associated Press tally, Mr Obama leads by 1,578 to 1,468. A candidate needs 2,024 delegates to win the nomination.