WASHINGTON (Reuters) - Republican U.S. Senator Ted Cruz of Texas, a Tea Party favorite seen as a potential 2016 presidential contender, on Thursday put Democrat Hillary Clinton's chances of winning the White House at 40 percent. "The media thinks she is unstoppable, but they also thought she was unstoppable in the 2008 Democratic primary," which Barack Obama won en route to the White House, Cruz said of the former secretary of state and wife of two-term U.S. President Bill Clinton. ~snip~ Cruz, who spoke at a Politico Playbook Breakfast, was pressed by moderator Mike Allen on whether he planned to...