He said Mahama's monumental defeat was self inflicted by himself and his campaign team.
Speaking on Adom FM, Spio-Garbrah said God cannot be the reason for the defeat.
He cited how the NDC, to date, has not been able to collate the 2016 election results even though it had a campaign team.
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John Mahama disclosed that he will seek the mandate to be NDC's flagbearer for the 2020 general elections last month.
During one of his campaign tours in the Central Region this week, he claimed that the NDC’s defeat was orchestrated by God.
Mr Mahama had said the defeat, which is the heaviest to be suffered by a sitting president since Ghana returned to democratic rule in 1992, was to afford Ghanaians the opportunity to compare the performance of his administration to that of the current regime led by Nana Akufo-Addo.