Secretary Julian Castro is defending Democratic presidential candidate Hillary Clinton over the inquiry into her State Department emails.

Castro, head of the Department of Housing and Urban Development, went on CNN's "State of the Union" to defend Clinton over her alleged mishandling of email correspondence while in the State Department. Castro is rumored to become Clinton's running partner in the upcoming presidential election.

"What you have with these emails is basically a witch hunt," Castro told Jim Acosta on Sunday. He said Congress and others had conducted various investigations into the Benghazi tragedy and found no wrong doing on Clinton's part.

"Congressman [Ted] Gowdy, who is leading this, is very intentionally trying to manipulate this witch hunt to play politics," Castro said. "That's unfortunate and it's one of the reasons Congress has a 19 percent approval rating."

Clinton has been calling for the State Department to release a large number of emails she exchanged while working as head of the department, including emails concerning the 2011 attack on the U.S. consulate in Benghazi, Libya, which caused the death of four Americans.

Last week the State Department released around a third of the emails to The New York Times. The emails show then Clinton did not receive classified information about the impending attack. This supports Clinton's claims; however, hundreds of more emails remain unseen.

Nonetheless, Sec. Castro's defense of Clinton comes days after it was suggested he join her on the presidential run for 2016.

Henry Cisneros, who ran the HUD during the Clinton administration, suggested Castro should join Clinton as running mate, calling him "the superior candidate considering his record, personality, demeanor and Latin heritage."

Acosta also asked Castro about Cisneros comments and reiterated a statement he made previously, deflecting a concise answer.

"If I had a dime for every amount of speculation that happens in D.C., you know, I think all of us would be wealthy," Castro said. "Who wouldn't be flattered by that."

Castro went on to explain he would continue focusing on his work, especially veteran homelessness.