With Pakistan's economy tanking and a Taliban insurgency raging, new president Asif Ali Zardari must choose if the time is right to risk more instability by entering a confrontation with old rival Nawaz Sharif.
A new power struggle is about the last thing the West would want in a nuclear-armed Muslim state whose backing is central to defeating al Qaeda and helping Nato stabilise Afghanistan.
Mr Zardari and Mr Sharif formed a coalition this year aimed at booting former army chief Pervez Musharraf out of the presidency, but after accomplishing that last month, their alliance collapsed and Mr Sharif became leader of the opposition.
Mr Sharif held the premiership twice in the 1990s, as did Mr Zardari's late wife, Benazir Bhutto, when their rivalry undermined democracy to a point that many people welcomed Mr Musharraf's coup in 1999.
Analysts fear vendettas from the past could haunt Pakistan.
If Mr Zardari and others "have revenge in mind, then the game is lost before it is begun", concluded Mr Ardeshir Cowasjee, one of Pakistan's most venerable columnists, in the Dawn newspaper on Sunday, a day after Zardari's election.
International lenders won't like giving billions of dollars to keep Pakistan afloat if they fear political battles will divert the government from putting finances in order.
"We don't care who becomes the president," Muhammad Hafiz, 70, told Reuters as he walked past a rally of celebrating Mr Zardari supporters in the southern city of Hyderabad.
"What we care about is security problems, and rising prices."
Inflation is running at nearly 25 per cent, and government borrowing needs to be cut drastically.
Authorities have imposed limits to prevent a freefall in a stock market that has plunged 40 per cent since peaking in April, the rupee is at all-time lows, and foreign currency reserves are so low, with €3.8 billion in central bank coffers, that the international bond market has priced in a possible default.
Ahsan Chishti, head of international institutional sales at Karachi-based brokerage house BMA Capital Ltd, saw a chance of better decision-making, with a president and a prime minister from the same party, but the right steps had to be taken quickly.
"Broader challenges will have to be subverted without delay for any sustainable market recovery," Mr Chishti said.
The margin of Zardari's victory in Saturday's vote by lawmakers from the upper and lower houses of Parliament and four provincial assemblies should afford him some sense of security.
But analysts say Mr Zardari needs a drastic image make-over. Though never convicted on various charges of corruption and murder, he spent 11 years in jail. He denies any wrongdoing.
"The challenges ahead are enormous," the News said in an editorial on Sunday.
"For a starter, he needs a quick and complete makeover of his image from a wily politician ... not mindful of whether he was breaking his promises or losing his credibility," it said.
How he handles the reinstatement of judges dismissed by Mr Musharraf last year will go some way to determining his credibility, as he has stalled on the issue so far.
Mr Sharif, the Prime Minister who was overthrown by Mr Musharraf, pulled his Pakistan Muslim League (Nawaz) (PML-N) party out of the coalition because of Mr Zardari's stalling on the question of the judiciary, just days after his usurper quit.
Eyes are now on Punjab, Pakistan's richest province, to see if Zardari tries to destabilise a PML-N provincial government.
The rivals could duck early confrontation while they build up war chests after a decade out of power.
"Unless the two sides realise that open confrontation will be harmful for both ... they will continue to move towards a bitter conflict," Hasan-Askari Rizvi, a political analyst, wrote in the Daily Times on Sunday, noting that the signs were ominous.
Mr Rizvi saw Mr Zardari's presidency hinging on the level of political support he gives the army in an unpopular struggle against the Taliban menace, and how the government addresses US worry about militant sympathisers in the intelligence apparatus.
A close adviser to Mr Zardari, who requested anonymity, characterised Mr Zardari's understanding with army chief General Ashfaq Kayani as: "We run the politics, you run the army. We won't interfere".
US Secretary of State Condoleezza Rice voiced optimism on Saturday that Mr Zardari would deliver in the war against militancy, which is the principal US interest in Pakistan.
A US commando raid on a Pakistani village last week and increasingly frequent missile attacks by drone aircraft on militants in Pakistani tribal lands have sparked uproar.