WASHINGTON (Reuters) - Dozens of Republican former U.S. national security officials are forming a group that will back Democratic presidential candidate Joe Biden, people familiar with the effort said, in a further sign that President Donald Trump has alienated some members of his own party. The group will publicly endorse Biden in the coming weeks and its members plan to campaign for the former vice president who is challenging Trump in the Nov. 3 election, the sources said. It includes at least two dozen officials who served under Republican Presidents Ronald Reagan, George H.W. Bush and George W. Bush, with...