By Jenna Zucker and Gabriella Borter BUFFALO, N.Y. (Reuters) -An investigation into the shooting of more than a dozen people in Buffalo, New York, turned on Monday to whether warning signs of the attack were missed, as public figures decried the suspect’s racist ideology and the spread of white supremacy. Authorities said Payton Gendron, 18, carried out an act of “racially motivated violent extremism” when he opened fire with a semi-automatic rifle on Saturday at the Tops Friendly Market in Buffalo, where 11 of the 13 struck were Black. Investigators have said they are searching through phone …