abuja nigeria atiku abubakar former vice president key ally president muhammadu buhari say sunday join country opposition party quit rule progressives congress apc last month abubakar first political heavyweight signal potential bid presidency could pit 74-year-old buhari buhari take power 2015 illness keep absent much year abubakar prepare run president 2019 spokesman say last month leave apc indicate sunday whether would try become opposition people democratic party pdp presidential candidate abubakar rejoin pdp four years resolve issue say accord statement sunday leave pdp believe long align principles equity democracy social justice say sunday statement abubakar criticize apc let nigerian people fail create strong economy job especially young one quarter 18-25 year olds unemployed former key ally nigeria 's buhari join opposition party