The centre-left leader proposes reforms to tackle corruption and create jobs, possibly with the backing of comedian Beppe Grillo, whose Five Star Movement won an unexpected 25% in the election and holds the balance of power.
They are now in disarray, after their commander in the east, known as Colonel Karuna, broke away early this month, complaining about the domination of the movement by northerners, and claiming the backing of several thousand Tiger fighters.
Yet the Afghan rebels also know that any open backing by Mr. Karzai's unpopular administration is likely to backfire, denting their movement's credibility.
Mr Kirchner is less popular than Mr Menem within his own Peronist movement, and owed much of his success in the first round to the backing of Mr Duhalde's party machine in Buenos Aires province.