Mr. Panetta was clearly attempting to defend President Obama's failure to negotiate a deal that would leave a residual US force in Iraq beyond the scheduled date for the US troop withdrawal.
But as I noted previously, during the 2008 Presidential debates, Mr. Obama made it perfectly clear that not only did he not have any problem with the prospect of Iran ultimately expanding its influence in Iran, he actually desired the aforementioned scenario:
After boasting that he would be willing to meet, without precondition, with the leaders of Iran, Syria, Venezuela, Cuba and North Korea, Obama went on to say:Good grief....
"I think that it is a disgrace that we have not spoken to them [the aforementioned leaders]. We’ve been talking about Iraq -- one of the first things that I would do in terms of moving a diplomatic effort in the region forward is to send a signal that we need to talk to Iran and Syria because they’re going to have responsibilities if Iraq collapses. They have been acting irresponsibly up until this point. But if we tell them that we are not going to be a permanent occupying force, we are in a position to say that they are going to have to carry some weight, in terms of stabilizing the region."
Hence, according to Obama, as soon as the US military packs its bags, leaves Iraq [completely] and tells Iran "that we are not going to be a permanent occupying force" in the country, Iran will then be able to fill the vacuum and help stabilize the country.