Sen. Barack Obama (Ill.), in his first day as the presumptive Democratic nominee, quickly found himself taking heat from both his rival and from a one-time Democratic vice presidential nominee.

After Obama’s speech to the American Israel Public Affairs Committee (AIPAC), Sen. Joe Lieberman (I-Conn.) slammed Obama for his foreign policy proposals and claims Obama flip-flopped on a vote made earlier this year.

In particular, Lieberman and the McCain camp criticized Obama for his opposition to a bill Lieberman co-sponsored designating the Iranian Revolutionary Guard a terrorist organization.

“I was hoping, and I continue to hope, that he will say that vote was a mistake,” Lieberman said.

Obama did say in his AIPAC speech Wednesday that the Iranian Revolutionary Guard’s Quds force “has rightly been labeled a terrorist organization.” His campaign said his reason for voting against Lieberman’s measure was because of language in the bill that would have kept troops in Iraq indefinitely.

Following Lieberman’s participation on the McCain conference call, he spoke to Obama on the Senate floor.

At the budget vote, Lieberman approached the Illinois senator for a handshake and a word. Obama immediately pulled Lieberman into a corner where the two could talk privately.

Sen. Joe Leiberman. Photo by Benjamin J. Myers

After a few minutes, Sen. Claire McCaskill (D-Mo.), sitting a few feet away, shouted to Obama to keep his voice to a minimum and pointed to the gaggle of reporters assembled at the ledge of the press gallery. The two men continued their discussion, then shook hands politely and even shared a half-hug.
Afterward, Obama told a reporter outside the Senate floor that he and Lieberman were “just talking politics.”

Speaking to a packed audience earlier in the day at AIPAC, Obama extolled the U.S.-Israeli relationship and offered tough talk on Iran. McCain has criticized Obama for saying he is willing to sit down with an Iranian president who threatens Israel’s existence and disputes the reality of the Holocaust.

“Contrary to the claims of some, I have no interest in sitting down without adversaries just for the sake of talking,” Obama said. He added later that there should be “no doubt: I will always keep the threat of military action on the table to defend our security and our ally Israel.”

McCain and his campaign have sought to portray Obama as weak on national security, particularly on the issue of Iran, as it became clear that Obama would likely be the Democratic nominee.

With the guesswork gone, the McCain campaign’s assault on Obama Wednesday was a clear sign that the general election has begun in earnest.

McCain and the Republican National Committee (RNC) have repeatedly criticized Obama for saying he would meet with U.S. adversaries, and in doing so, they have specifically pointed to Iranian President Mahmoud Ahmadinejad as an example of one of those meetings.

Any belief on the part of Jewish voters that Obama is any less than 100 percent committed to Israel’s security or is willing to appease Ahmadinejad would cripple the Illinois senator’s chances with that key demographic, particularly in a crucial state like Florida.

Jared Allen contributed to this article.