By Jeff Mason CHICAGO (Reuters) - U.S. President Barack Obama said on Wednesday he was "heartbroken" that another shooting had occurred at the Fort Hood Army base in Texas. "We are going to get to the bottom of exactly what happened," Obama told reporters in Chicago, where he was traveling for Democratic fundraisers. "We're heartbroken that something like this might have happened again." On his flight back to Washington, Obama held a conference call with the Defense Department and FBI about the shooting, the White House said. Participants included Secretary of Defense Chuck Hagel, Chairman of the Joint Chiefs of Staff Martin Dempsey, and FBI Deputy Director Mark Giuliano.