Read: Election Class of 2016—Why America Is Waiting for Joe BidenVice President Joe Biden was a guest on The Late Show with Stephen Colbert Thursday, where he opened up to the host about his son's death and whether he'll run for president in 2016."I want to talk about the elephant in the room which, in this case, is a donkey," joked Colbert. "You said this weekend you're not sure if you're emotionally prepared to run for president," referring to Biden's first public comments about a potential run.Biden reiterated that he and his family are still struggling after the loss of his oldest son, Beau, to brain cancer this year. To run for president, Biden said, he'd have to promise the American people that they "have my whole heart, my whole soul, my energy, and my passion to do this." He's not sure he can commit to that yet.Biden got emotional, tearing up as he shared stories about Beau with the late-night host."I met with a group of military families," Biden said. It was "going great" until, he recalled, a man yelled, "'Major Beau Biden. Bronze Star, sir! Served with him in Iraq.'"All of the sudden, I lost it," Biden admitted. "You can't do that."