Obama was already onboard his campaign plane when Clinton arrived. They greeted each other, stood in the aisle chatting for several minutes. Clinton then took her seat in the first row on the right side of the plane while Obama sat in the second row on the left. Neither spoke with reporters also aboard the campaign plane.
As he sought Clinton's full support after she suspended her campaign last month, Obama encouraged his donors to help the former first lady retire debt from her unsuccessful bid for the nomination. After a monthslong, divisive primary battle, the two have been trying to unite their party ahead of the November election against Republican John McCain.
Clinton has been mentioned as a potential running mate for Obama. Earlier Wednesday, Clinton deflected a reporter's inquiry about whether she has turned over documents for her former rival's campaign to review as part of the vice presidential search.
Obama, meanwhile, had made an unannounced stop at a downtown Washington building that houses the law firm of another member of his vice presidential search team, Eric Holder, but he wouldn't say why.
Both Obama and McCain have been trying to keep a tight lid on their searches, including only a small handful of top aides in the discussions to make sure the vetting process is as discrete as possible.
Earlier Wednesday the campaign was dominated by news that Iran has test-fired nine missiles, including ones capable of hitting Israel, making a dramatic show of its readiness to strike back if the United States or Israel attacks it over its nuclear program.
McCain said Iranian missile tests Wednesday were a "serious escalation," but agreed with Obama that lines of communication with Tehran should stay open even as the U.S. seeks more painful economic sanctions on the theocratic Islamic regime.
The United States claims Iran is intent on developing nuclear weapons to bolster a military arsenal which could threaten the wider Middle East, Israel in particular. Tehran also is accused of deep involvement in Iraq, where U.S. commanders say Iran is training and arming rogue Shiite Muslim fighters for attacks on American.
Regardless of the outcome of the U.S. election, Iran figures to be one of the thorniest foreign policy issues confronting the next American commander in chief.
McCain, who prides himself on his experience in security matters and foreign affairs, said the latest Iranian military muscle-flexing was "a serious escalation" because "an attack on Israel would lead to a wider war including American involvement."
While implying that Obama's Iran policy would offer "unilateral concessions that undermine multilateral diplomacy," McCain agreed that diplomacy and stiffer economic sanctions remained the weapon of choice in altering Iranian bellicosity.
In a conversation with reporters on his campaign bus in Pennsylvania, the Arizona senator said "lines of communications" should continue but be paired with sanctions to alter Iran's "very aggressive behavior, not only rhetorically, but in their pursuit of nuclear weapons as well as this latest missile test."
McCain said there is "continuing, mounting evidence that Iran is pursuing the acquisition of nuclear weapons," a statement that appears at odds with a December U.S. intelligence report.
The National Intelligence Estimate concluded that Iran's nuclear weapons development program has been halted since the fall of 2003 because of international pressure. The report cautioned that Iran continues to enrich uranium and still could develop a bomb between 2010 and 2015 if it decided to do so.
Asked how he would respond to Wednesday's test if he were president, Obama said he would confer with his national security team to find out whether "this indicates any new capabilities on Iran's part."
"At this point, the report is unclear, it's still early," Obama said. "What this underscores is the need for ... a clear policy that is putting the burden on Iran to change behavior. And frankly, we just have not been able to do that the last several years, partly because we're not engaged in direct diplomacy."
Obama said he continued to favor an incentive package that is aimed at getting Iran to drop its nuclear ambitions.
The Iranian missile tests Wednesday and reports earlier this week that Iraq's American-backed government wants a three- to five-year timeline for U.S. troops to withdraw, had broken the campaign focus on the struggling economy but the troubles showed no signs of easing Wednesday.
The Dow Jones industrial average tumbled more than 230 points - with key financial stocks particularly hard hit. Americans continued to face rising and record gasoline prices, a swarm of home mortgage foreclosures, rising food costs and growing unemployment.
