Hillary Clinton’s exclusive use of a personal email account to conduct work while she served as secretary of state is “highly unusual,” especially considering how many times cabinet leaders are told to preserve government correspondence, said former White House Press Secretary Robert Gibbs on Tuesday.

“I think it’s something they’re going to have to explain in good measure today and probably figure out how to get a lot of those emails, or as many as they can back into the archive,” said Gibbs, who served as President Obama’s first press secretary.

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The New York Times reported Monday evening that Hillary Clinton used a personal email account exclusively to conduct work during her time as Secretary of State. The move raises questions about whether it violated federal law and hampers the government's ability to archive correspondence by Clinton, who is expected to make another White House run.

Gibbs said White House officials attend numerous briefings informing them about the need to preserve their email, “making sure it’s part of your official account.” He admitted the discovery opens the opportunity for Clinton critics to go on attack.

“I think it’s much easier for critics to explain why they don’t exist than it might be for her to explain why she used her private email,” he said.

Gibbs also downplayed the impact Israeli Prime Minister Benjamin Netanyahu’s speech Tuesday to a joint session of Congress will have on an already shaky relationship with the Obama administration. The prime minister will address Obama’s ongoing negotiations with Iran over its nuclear program. Netanyahu believes the White House effort poses a danger to Israel. Obama advisors say Netanyahu is interfering with American foreign policy efforts.

“Even though there are great disagreements, and I think the strain in that relationship is as deep as maybe It has ever been, I think there are still a lot of common issues that they’ll have to work on,” Gibbs said.

Congress may end having a role in any Iranian deal so negotiations are at the beginning stage, Gibbs said.

“These two powers are going to have to work together and they’re going to have find a way past those personalities in order to do that,” Gibbs said.