The opposition Movement for Democratic Change has insisted that it must have sole control of the ministry, which brings with it authority over the police, if power-sharing is to be meaningful.
But around 14 hours after talks started at a Southern African Development Community summit in Johannesburg, the organisation’s secretary-general Tomaz Salamao emerged to say: "Summit decided that the inclusive government be formed forthwith [and] the ministry of home affairs be co-managed between Zanu-PF and MDC-Tsvangirai."
Mr Mugabe had earlier proposed the joint ministers concept himself, and agreed to the proposal, but Mr Tsvangirai’s MDC rejected it.
A source inside the meeting described Mr Mugabe as "extremely contemptuous" of Mr Tsvangirai, interrupting him during his presentation. When the MDC leader said he had won the March 29 election, in which he came first, Mr Mugabe shouted "You didn’t! You didn’t!"
"Our situation is not a domestic issue, it is a foreign issue," Mr Mugabe told the heads of state, expounding on his anti-Western mindset. "Home affairs is part of security and I as president have greater superintendence."
Afterwards, Mr Tsvangirai declared: "The concept of co-ministering cannot work." With two competing ministers Mr Mugabe’s Zanu-PF party would be in a position to sideline the MDC, as the upper levels of the bureaucracy are its own members, and it would also threaten the MDC’s one-vote majority in cabinet under the political agreement.
Mr Tsvangirai said: "Perversely, pressure was brought to bear on the MDC, a party that won an election but has shown compromise and political maturity in these negotiations rather than the party that lost an election and has flouted the spirit and substance of the agreement, namely Zanu PF.
"Mr Mugabe is not the President of Zimbabwe without this agreement," he added, saying that the MDC "hope and pray that the guarantors of the agreement, in particular progressive members of SADC and the African Union, will now move very quickly to try and salvage this agreement".
Zanu-PF has already overseen the destruction of Zimbabwe’s economy and the killing of almost 200 opposition supporters over the election season earlier this year.
The summit decision leaves the entire process on the verge of collapse. Mr Salamao said: "SADC was asked to rule and SADC took a decision, that’s the position of SADC. It’s up to the parties to implement." It is also a demonstration, yet again, of Mr Mugabe’s extraordinary skills as a political operator, having convinced his colleagues, who are the guarantors of the power-sharing agreement, to force Mr Tsvangirai into a corner.