JOHNSTOWN, PA - JULY 30: (L-R) Democratic vice presidential nominee U.S. Sen Tim Kaine (D-VA), former U.S. president Bill Clinton and democratic presidential nominee former Secretary of State Hillary Clinton greet supporters during a campaign rally at Johnstown Wire Technologies on July 30, 2016 in Johnstown, Pennsylvania. Hillary Clinton and Tim Kaine are continuing their a three-day bus tour through Pennsylvania and Ohio. (Photo by Justin Sullivan/Getty Images)

JOHNSTOWN, PA - JULY 30: Democratic presidential nominee former Secretary of State Hillary Clinton speaks during a campaign rally with democratic vice presidential nominee U.S. Sen Tim Kaine (D-VA) at Johnstown Wire Technologies on July 30, 2016 in Johnstown, Pennsylvania. Hillary Clinton and Tim Kaine are continuing their a three-day bus tour through Pennsylvania and Ohio. (Photo by Justin Sullivan/Getty Images)

BEVERLY HILLS, CA - JULY 30: Professor of Space Technology at Georgia Institute of Technology and MARS Consulting Scientist Dr. Robert Braun speaks onstage during the 'National Geographic Channel - MARS' panel discussion at the National Geographic Channels portion of the 2016 Television Critics Association Summer Tour at The Beverly Hilton Hotel on July 30, 2016 in Beverly Hills, California. (Photo by Frederick M. Brown/Getty Images)

JOHNSTOWN, PA - JULY 30: A young girl looks on during a campaign rally with democratic presidential nominee former Secretary of State Hillary Clinton and democratic vice presidential nominee U.S. Sen Tim Kaine (D-VA) at Johnstown Wire Technologies on July 30, 2016 in Johnstown, Pennsylvania. Hillary Clinton and Tim Kaine are continuing their a three-day bus tour through Pennsylvania and Ohio. (Photo by Justin Sullivan/Getty Images)

JOHNSTOWN, PA - JULY 30: Democratic presidential nominee former Secretary of State Hillary Clinton (R) looks on as democratic vice presidential nominee U.S. Sen Tim Kaine (D-VA) speaks during a campaign rally at Johnstown Wire Technologies on July 30, 2016 in Johnstown, Pennsylvania. Hillary Clinton and Tim Kaine are continuing their a three-day bus tour through Pennsylvania and Ohio. (Photo by Justin Sullivan/Getty Images)

JOHNSTOWN, PA - JULY 30: Democratic presidential nominee former Secretary of State Hillary Clinton looks on during a campaign rally with democratic vice presidential nominee U.S. Sen Tim Kaine (D-VA) at Johnstown Wire Technologies on July 30, 2016 in Johnstown, Pennsylvania. Hillary Clinton and Tim Kaine are continuing their a three-day bus tour through Pennsylvania and Ohio. (Photo by Justin Sullivan/Getty Images)

JOHNSTOWN, PA - JULY 30: Steel workers look on during a campaign rally with democratic presidential nominee former Secretary of State Hillary Clinton and democratic vice presidential nominee U.S. Sen Tim Kaine (D-VA) at Johnstown Wire Technologies on July 30, 2016 in Johnstown, Pennsylvania. Hillary Clinton and Tim Kaine are continuing their a three-day bus tour through Pennsylvania and Ohio. (Photo by Justin Sullivan/Getty Images)

JOHNSTOWN, PA - JULY 30: A young girl looks on during a campaign rally with democratic presidential nominee former Secretary of State Hillary Clinton and democratic vice presidential nominee U.S. Sen Tim Kaine (D-VA) at Johnstown Wire Technologies on July 30, 2016 in Johnstown, Pennsylvania. Hillary Clinton and Tim Kaine are continuing their a three-day bus tour through Pennsylvania and Ohio. (Photo by Justin Sullivan/Getty Images)