The former Clinton staffers, who have worked for Clinton for a combined 10 years, thanked "tens of thousands" of supporters who they said petitioned, called and wrote letters to Obama, urging him to pick Clinton as his running mate.
"Because of your work, Senator Obama asked Hillary to be his keynote speaker at the Democratic National Convention," Arora and VoteBoth.com co-founder Adam Parkhomenko wrote on their Website. "Regretfully, this means that Senator Hillary Clinton is no longer under consideration as Senator Obama's running mate."
Parkhomenko is a former executive assistant to Patti Solis Doyle, Clinton's former campaign manager who was fired in February and now works for the Obama campaign, awaiting the presumptive Democratic nominee's vice-presidential pick, whom she will serve as chief of staff.
Arora, a former Clinton campaign press aide, is now attending law school.
Officially, the Democratic convention speaker schedule has not been publicly released. And the Obama campaign is keeping the details of whom they are considering as a potential vice presidential candidate a closely guarded secret.
"The schedule for the convention has not been finalized," Obama spokesperson Bill Burton told ABCNews.com. "We're not commenting about the nominee selection process."
But Nedra Pickler of The Associated Press has reported that Obama and Clinton advisers have said Clinton is likely to speak on the second night of the party's August convention in Denver -- coinciding with the anniversary of the ratification of the amendment giving women the right to vote.
Obama spent several hours this week meeting with the co-chairs of his vice presidential committee search team Eric Holder and Caroline Kennedy in Washington.
Potential Democratic vice-presidential contenders include Virginia Gov. Tim Kaine, Indiana Sen. Even Bayh, Delaware Sen. Joe Biden, New Mexico Gov. Bill Richardson and Sebelius, a two-term governor of a traditionally red state, and McCaskill, a first-time senator from a battleground state who is close to Obama.
McCaskill campaigned with Obama in Missouri on Wednesday, but she has said she's not being vetted, and sources close to her describe her role as a close personal advisor rather than a possible veep candidate.
This week Sebelius sidestepped speculation about being on Obama's vice-presidential short-list.
"All the information on the vice-presidential process is really being answered by the campaign," Sebelius told a Kansas ABC affiliate on Tuesday.
While Washington reporters are busily chasing rumors about who's on Obama's veep short-list, voters may be less interested.
McCain and Obama's choice of running mates ranked dead last in importance among voters polled recently by ABC News, with only 15 percent of likely voters calling the candidates' veep choice "extremely important."
Of far greater concern to voters is the economy, gas prices and the Iraq war, according to the latest Washington Post/ABC News poll.
Even among Clinton's primary supporters, only 24 percent said the choice of a running mate would be extremely important in their vote in November.
And Clinton's name on the ticket wouldn't necessarily boost Obama's support.