He joined the ruling APC and sought the party's ticket in 2014, but lost to Gen Buhari at the primary held in Lagos.
Like all 11 other presidential aspirants of the party, Dankwambo is presently in Port Harcourt, Rivers State, where the National Convention of the PDP is ongoing.
He has long enjoyed support from the business elite in Nigeria's commercial capital Lagos for his conservative-capitalist ideals and, as vice president in a PDP administration from 1999-2007, implemented a programme of liberalisation in areas including the telecoms sector.
"I can not do it alone", Mr Abubakar said in his acceptance speech.
According to Daily Post, Wike said that the PDP primaries will go smoothly despite APC's plot.
However, it added that the Sokoto governor "offers the best chance of appealing to the critical northwestern and northeastern voting bloc, and that he will be Buhari's strongest challenger".
I want to thank Governor Okowa for planning and organizing this transparent, free and fair Presidential Primary and Convention.
"More importantly, let me congratulate the victor and new flagbearer of our party and all the fellow aspirants for running credible and mature campaigns and working all along to reassure millions of our fellow party members and other Nigerians that PDP will leave the convention venue more united and ready to work together to form the next government at the federal and other levels in a manner that we will unite the country, grow the economy, carry along all stakeholders, empower the youths and make government serve the people better". The event in Port Harcourt between yesterday and today was a victory for Nigeria and for democracy.
"Our warning to political thugs and other hoodlums is that they should stay away from the venue and even the entire state", state police spokesman Nnamdi Omoni told AFP.
He said "As at thursday, APC brought hoodlums to create an atmosphere of insecurity in Rivers State".
The presidential flagbearer of the party will emerge from the convention.
Buhari indicated in April that he planned to run for a second term.
The retired general, who headed a military regime in the 1980s, has faced growing pressure to step down because of failing health after spending several months in London a year ago receiving treatment for an undisclosed ailment.
Voters in the former British colony will elect governors and lawmakers as well as the president in elections set for February and March next year.