Some members of the opposition MDC Alliance are plotting to topple leader Nelson Chamisa at the party’s next congress in 2019, a newspaper has reported.Chamisa narrowly lost the July 30 presidential polls to Emmerson Mnangagwa but has challenged the result, alleging vote rigging.Chamisa is blamed by some insiders for failing to unite the party, which saw more than one MDC Alliance candidate fielded in some parliamentary constituencies, NewsDay said. Campaign 'blunders'"The plan is premised on two pillars, one to blame Chamisa and the alliance for failing to deal with double nominations, which allowed Zanu-PF to get a two-thirds majority in the National Assembly and, secondly, to ramp up pressure on Chamisa by blaming his electoral defeat at the hands of Zanu-PF on his campaign blunders," the source told the paper.Chamisa came in for criticism for some of his exaggerated campaign messages, such as his claim in January that President Donald Trump had promised $15bn to Zimbabwe if the MDC won the polls.Party tensionsThe US embassy in Harare publicly denied the claim.According to the NewsDay report, the party’s secretary general, Douglas Mwonzora, was considered an option to replace Chamisa.Last week the state-run Herald ran a story claiming there are tensions between Mwonzora and Chamisa. But Mwonzora has denied this. He said last week via Twitter that he is suing the Herald, describing its story as "malicious" and "false".The story in the Herald of today suggesting that there is infighting between @nelsonchamisa and myself post election is false and malicious. It is typically designed to sow seeds of division within the MDC Alliance. I remain focused on the People's struggle.— Douglas Mwonzora (@DMwonzora) August 6, 2018Today I have formally sued The Herald over the false story it published yesterday. I seek exemplary damages over the malicious story. While as a constitution maker I respect freedom of expression I think malicious reporting must be punished.— Douglas Mwonzora (@DMwonzora) August 7, 2018 Chamisa took over control of the MDC after the death of veteran leader Morgan Tsvangirai in February. At Tsvangirai’s funeral Chamisa vowed to quit politics if he lost to Mnangagwa, NewsDay reported at the time.