The presidential candidate said he planned to do more in the days ahead to raise doubts about his opponent's claims to foreign policy and other Washington experience. In a television ad that her campaign credits with helping her win, she portrayed herself as most prepared to handle an international crisis.
"What exactly is this foreign policy experience?" Obama asked mockingly. "Was she negotiating treaties? Was she handling crises? The answer is no."
Clinton, who was asked in TV interviews Wednesday about her national security qualifications, ticked off a series events in which she played a role, including peace talks in Northern Ireland, the Kosovo refugee crisis and standing up for women's rights in China. She also cited her work on the Senate Armed Services Committee.
Obama's campaign immediately delivered on his pledge to criticize Clinton. Aides distributed a memo and held a conference call to question why she won't release her tax returns. The Clinton campaign responded with a statement e-mailed to reporters while they were on the Obama call that said the Clintons' returns since they left the White House will be made public around April 15.
Obama reflected on the losses that broke a 12-contest winning streak in a talk with reporters aboard his campaign plane as he returned to his hometown of Chicago from San Antonio.
"There's no doubt that Senator Clinton went very negative over the last week," Obama said. He said the Clinton campaign's multiple attacks "had some impact" on the election results "particularly in the context where many of you in the press corps had been persuaded that you had been too hard on her and too soft on me."
"Complaining about the refs apparently worked a little bit this week," he said, equating members of the news media with referees in a sporting event.
"So hopefully in addition to my call to Lorne Michaels, hopefully now people feel like everything's evened out and we can start actually covering the campaign properly," he said.
Obama spokeswoman Jen Psaki said the reference to Michaels, producer of the television comedy show "Saturday Night Live," was a joke. The show has recently featured skits in which actors portraying reporters lob softball questions at an Obama impersonator and hardball ones at a Clinton character. Clinton herself appeared on the show last weekend. Obama was on the show last November.
Obama also complained about what he said was "the notion that somehow all the states I win somehow are not bellwether states but the states that Senator Clinton wins, those are the critical ones."
He said it was "a strange way of keeping score and I don't think it makes much sense."
As to tactics ahead, Obama said that Clinton "made a series of arguments on why she should be a superior candidate. I think it's important to examine that argument."
"We're happy to join the debate, If that's the debate they want to have," Obama said, noting Clinton's efforts to portray him as lacking her level of experience. "In the coming weeks, we will join her in that argument."
Obama also brushed off a question about a joint ticket with Clinton. "We are just focused on winning this nomination," he said. "I think it is premature to start talking about a joint ticket."
Obama had nothing on his public schedule Wednesday and Thursday. Friday, he flies to Wyoming to campaign and was also expected to go to Mississippi over the weekend - sites of the next two Democratic contests.