OMAHA, Neb. -- Calling himself a conservative, pro-life Republican, Ameritrade Chief Operating Officer Pete Ricketts Saturday joined the Republican primary race for the U.S. Senate. He said he grew up with great values and tremendous opportunities, and he wants his three children and other people's children to have the same opportunities he had. Ricketts said issues important to him include tax reform, national defense, international trade and modernization of Social Security. Ricketts, 40, faces two other Republicans: former Nebraska Attorney General Don Stenberg and former state GOP Chair David Kramer. The primary winner likely would face Democratic U.S. Sen. Ben...