US President Barack Obama speaks at a press conference at the Pentagon in Washington, DC on August 4, 2016. / AFP PHOTO / Brendan SmialowskiBRENDAN SMIALOWSKI/AFP/Getty Images

Retired US Navy Intel and Arizona Air Guard servicemember Nate Terani (C) alongside fellow veterans, carries empty boxes serving as a symbolic delivery of signatures on a petition calling for Senator John McCain(R-AZ) and other Republican leaders to withdraw their endorsement of Republican presidential nominee Donald Trump on August 4, 2016 on Capitol Hill in Washington,DC. The event is organized by military veterans, MoveOn.org and Common Defense PAC,and the signatures were actually delivered on a USB thumb-drive. / AFP PHOTO / SAUL LOEBSAUL LOEB/AFP/Getty Images

Veterans stand alongside empty boxes serving as a symbolic delivery of signatures on a petition calling for Senator John McCain(R-AZ) and other Republican leaders to withdraw their endorsement of Republican presidential nominee Donald Trump on August 4, 2016 on Capitol Hill in Washington,DC. The event is organized by military veterans, MoveOn.org and Common Defense PAC,and the signatures were actually delivered on a USB thumb-drive. / AFP PHOTO / SAUL LOEBSAUL LOEB/AFP/Getty Images

Empty boxes serving as a symbolic delivery of signatures on a petition calling for Senator John McCain(R-AZ) and other Republican leaders to withdraw their endorsement of Republican presidential nominee Donald Trump on August 4, 2016 on Capitol Hill in Washington,DC. The event is organized by military veterans, MoveOn.org and Common Defense PAC,and the signatures were actually delivered on a USB thumb-drive. / AFP PHOTO / SAUL LOEBSAUL LOEB/AFP/Getty Images

Retired US Navy Nuclear Machinist Mate 2nd Class Jim Lyons (C), alongside fellow veterans, carries empty boxes serving as a symbolic delivery of signatures on a petition calling for Senator John McCain(R-AZ) and other Republican leaders to withdraw their endorsement of Republican presidential nominee Donald Trump on August 4, 2016 on Capitol Hill in Washington,DC. The event is organized by military veterans, MoveOn.org and Common Defense PAC,and the signatures were actually delivered on a USB thumb-drive. / AFP PHOTO / SAUL LOEBSAUL LOEB/AFP/Getty Images

Retired US Navy Nuclear Machinist Mate 2nd Class Jim Lyons (C), alongside fellow veterans, carries empty boxes serving as a symbolic delivery of signatures on a petition calling for Senator John McCain(R-AZ) and other Republican leaders to withdraw their endorsement of Republican presidential nominee Donald Trump on August 4, 2016 on Capitol Hill in Washington,DC. The event is organized by military veterans, MoveOn.org and Common Defense PAC,and the signatures were actually delivered on a USB thumb-drive. / AFP PHOTO / SAUL LOEBSAUL LOEB/AFP/Getty Images

Retired US Navy Nuclear Machinist Mate 2nd Class Jim Lyons (C), carries empty boxes serving as a symbolic delivery of signatures on a petition calling for Senator John McCain(R-AZ) and other Republican leaders to withdraw their endorsement of Republican presidential nominee Donald Trump on August 4, 2016 on Capitol Hill in Washington,DC. The event is organized by military veterans, MoveOn.org and Common Defense PAC,and the signatures were actually delivered on a USB thumb-drive. / AFP PHOTO / SAUL LOEBSAUL LOEB/AFP/Getty Images

Retired US Navy Nuclear Machinist Mate 2nd Class Jim Lyons (R), retired US Marine Sergeant Alexander McCoy (2nd R), alongside fellow veterans, carries empty boxes serving as a symbolic delivery of signatures on a petition calling for Senator John McCain(R-AZ) and other Republican leaders to withdraw their endorsement of Republican presidential nominee Donald Trump on August 4, 2016 on Capitol Hill in Washington,DC. The event is organized by military veterans, MoveOn.org and Common Defense PAC,and the signatures were actually delivered on a USB thumb-drive. / AFP PHOTO / SAUL LOEBSAUL LOEB/AFP/Getty Images