They are the UPA's dynamic duo and both are PMs. Manmohan Singh is of course the Prime Minister while the Congrss President is called by precocious Congressmen as the 'Prime Monitor', all in good humour of course.

Both arithmetic and chemistry are required to win elections. And the made-for-each-other couple led the UPA to a memorable and somewhat unexpected victory in 2004. The UPA in its first innings saw the two reluctant politicians rewrite the rules of the game and introduce the concept of 'inclusive growth' to the country's political lexicon.

The general election in 2009 turned out to be even more remarkable. The Congress touched the magic figure of 200 in the Lok Sabha after many years. It fared better than expected in the battle for Uttar Pradesh, West Bengal and Maharashtra and there was a new confidence in the re-jigged UPA II. In its new avatar the alliance had quietly jettisoned troublesome allies like Lalu Prasad Yadav and Shibu Soren and yet did well on their home-turf. Sonia and Manmohan were on a song.

They looked even more confident in their second innings together. But a year later, the fault-lines are showing. The alliance looks a little frayed, more fragile and vulnerable. Political circles seem to be agog with speculation over perceived differences between the two PMs. The coalition is forced to dance to the tunes of Mamata Banerjee and M Karunanidhi and had to scramble to secure the support of Mulayam Singh Yadav, Lalu and Mayawati in Parliament.

But still the two remain the UPA's USP. Take them out and the alliance loses much of its appeal and credibility. Despite their 14-year age gap, the two seem to have developed a working relationship that is the despair of the principal opposition party, the BJP. Both being intensely private persons, they do not wear their emotions on their sleeves and both often look inscrutable like the Buddha. While he has steered the economy through the global meltdown and recession, Sonia and son Rahul have taken upon themselves the task of revitalising the Congress, hold organisational elections and reach out to the people. While the US President is said to have addressed Singh as 'The Guru', Sonia complements his administrative experience with her political instincts.

Senior bureaucrats marvel at the Prime Minister's eye for details and his capacity to wade through voluminous official reports. Officials who line up every week to brief him ahead of the meeting of the Union Cabinet, have come to dread his wry smile and the withering look. Nothing, they say, escapes his attention and very often he points out obscure but vital details overlooked by them.

The Prime Minister has gone out of his way to accommodate Sonia Gandhi's pet projects like the National Rural Employment Guarantee Scheme and the loan waiver for farmers. In return he was given a free hand to negotiate the Indo-US civil nuclear deal and the peace process with Pakistan.

Sonia Gandhi had to ride out several storms during UPA's first innings. She has come a long way since she was mocked at as a reader of public speeches. She has turned problems into opportunities and foes into friends. In the process, she has revived the fortune of the Congress and re-established the sway of the family over the party. Now as the NAC Chairperson she would be in a position to summon senior bureaucrats and the opposition would certainly look for an opportunity to accuse her of interfering in government and being an extra-constitutional authority.

While the Prime Minister publicly stated that he wished to include Rahul Gandhi in the Union Cabinet, Sonia clearly had a different opinion. But the PM appears to be genuinely fond of Rahul and seems to share a warm relationship with him.

Manmohan Singh and Sonia Gandhi do not agree on everything though. Their differences over the amendments to the Right to Information ( RTI) Act are not a state secret. While he strongly feels the amendments are necessary and that the judiciary needs to be kept out of its purview, she feels equally strongly that the Act should remain as it is.

They also do not seem to see eye to eye on how to deal with the Maoist menace or on the introduction of genetically modified crops like Bt Brinjal. The PM's reservations over a caste-based census and the Women's Reservation Bill are also fairly well known. But the two leaders have learnt to paper over such differences and work jointly in the interests of the alliance and the government. Manmohan Singh is the most trusted politician in the country and people are convinced that he would not accept anything that compromises the interests of the country.

The two reluctant politicians are the unlikely UPA openers and, to borrow a cricketing term, offer a straight bat. They may not have the flamboyance for 20-over cricket but the dour duo are in it for the long haul.