ABUJA (Reuters) - Nigeria s Atiku Abubakar, a former vice president and key ally of President Muhammadu Buhari, said on Sunday he had joined the country s opposition party after quitting the ruling All Progressives Congress (APC) last month.  Abubakar is the first political heavyweight to signal a potential bid for the presidency, which could pit him against the 74-year-old Buhari. Buhari took power in 2015, but illness has kept him absent for much of this year. Abubakar is prepared to run for president in 2019, a spokesman said last month when he left the APC. He  did not indicate on Sunday whether he would try to become the opposition People s Democratic Party s (PDP s) presidential candidate. Abubakar rejoined the PDP after four years because it has resolved its issues, he said, according to a statement on Sunday. He had left the PDP because he  believed it was no longer aligned to the principles of equity, democracy and social justice,  he said. In Sunday s statement, Abubakar criticized the APC for letting down the Nigerian people by failing to create a strong economy and jobs, especially for the young, with one quarter of 18-25 year olds unemployed. 
Former key ally of Nigeria's Buhari joins opposition party