(FILES) This file photo taken on March 18, 2015 shows US Agriculture Secretary Tom Vilsack speaking at a press conference in Washington, DC on March 18, 2015. US Democratic presidential candidate Clinton is expected to reveal her vice presidential pick by July 23, when she campaigns in Florida. Vilsack has known the Clintons for decades, and the candidate is said to have deep trust in him. A native of Pittsburgh, he could help carry the crucial swing state of Pennsylvania. / AFP PHOTO / NICHOLAS KAMMNICHOLAS KAMM/AFP/Getty Images