Opinion polls show the former security minister is the only candidate whose support is growing. A poll published on Friday by Indonesian non-government group Soegeng Sarjadi Syndicated said Mr Yudhoyono, with 44 per cent support, was more than twice as popular as President Megawati Soekarnoputri with 21 per cent.
Mrs Megawati's Indonesian Democratic Party of Struggle was routed in the legislative elections on April 5, losing almost half its supporters, many of whom voted for Mr Yudhoyono in an apparent protest at the level of corruption in the big parties.
And in a question about who would be the best vice-presidential candidate, Mr Kalla came top with 21 per cent while Hamzah Haz, the current Vice-President and possible running mate for Mrs Megawati, received 5 per cent support.
Sukardi Rinakit from the survey group said the results showed a Yudhoyono/Kalla team was preferred.
Mr Kalla, a business tycoon from South Sulawesi province, is regarded by many observers as Golkar's most popular candidate. His decision to pull out of the convention and join Mr Yudhoyono seems certain to split the Golkar vote in the July poll.
Polling is new in Indonesia (it as not really needed under Suharto) and it's accuracy is not always brilliant. If Yudhoyono is already at 44% he needs to pick up only another 6 points before 5 July. Kalla's supporters will contribute to that.
Golkar's legislative vote of 20% (even without any Kalla defectors) is not enough to overtake Megawati in the race to be the other candidate to go into the second round if one is necessary. By the looks of it the list of presidenciables is fast shrinking to Yudhoyono and Megawati.