But as polls near, signs of a rift have increasing bled through the tailored-for-the-public unity, with the government's confused response to the Evidence Act amendment serving as the most apparent example yet.
Following online protests against Section 114A of the Evidence Act, Najib who was in Saudi Arabia had on Aug 14 announced on Twitter that he would instruct the cabinet to review the controversial law.
A day later, Muhyiddin who chaired the cabinet meeting in Najib's absence decided against the review.
Malaysiakini had learnt that Muhyiddin also agreed to reprimand deputy ministers Saifuddin Abdullah (right) and Gan Ping Sieu as well as Umno Youth chief Khairy Jamaluddin for voicing out against the law.
Minister in the Prime Minister's Department Mohd Nazri Abdul Aziz confirmed this but said that it was merely a suggestion which Najib had rejected after chairing the cabinet meeting again on Aug 28.
"The prime minister was not around then. So the cabinet meeting today (Wednesday) chaired by the prime minister discussed this issue again and decided not to take further action," Nazri had said.
Despite the premier's final word, Muhyiddin on Sept 3 summoned the two deputy ministers to his office.
This was again confirmed by Nazri who was present at the meeting but said no reprimand was issued.
The de facto law minister was quick to add that he had not summoned the deputy ministers but was invited by Muhyiddin to explain the law to the duo.
Leaked documents to put Najib in a spot?
Behind the scenes, political machinations at the party level also appear to be at work.
According to PKR sources, it is believed that an Umno faction aligned to Muhyiddin was responsible for leaking the Ampang LRT line extension documents which points to Najib's alleged hand in the controversial award to George Kent (Malaysia) Bhd.
PKR had used the documents to put the premier in a spot by alleging that Najib had intervened in the project's open tender process in favour of George Kent consortium which chairperson Tan Kay Hock has been described as the former's golfing buddy.
When contacted, PKR directior of strategy Rafizi Ramli, who was responsible for exposing the scandal, said the documents were anonymously dropped off at the PKR headquarters.
"Unlike the National Feedlot Corporation documents where I had spoken to some people, the George Kent documents was dropped at the PKR headquarters in an envelope.
"All the documents were complete so it was up to me on how to make use of them. As to who was behind the documents, that's a subject of speculation." said Rafizi (right).
The contradictory signals sent out by the government - sometimes dismissed as simply another case of flip-flopping - may be derived from Najib's and Muhyiddin's contrasting approaches and styles of leadership.
This was apparent when the the premier who conceived the 1Malaysia slogan was forced to dodge a simple question: "Are you a Malaysian first, or are you a Malay first?"
"I won't respond in a way that will divide me and my deputy. In Malaysia, that can be very dangerous," Najib had replied at a student conference July last year.
He was referring to Muhyiddin's response to the exact question in 2010 where the deputy prime minister declared himself as Malay first.
Clash of ideologies
For the Umno old guards still nostalgic about former premier Dr Mahathir Mohamad's era, Muhyiddin, 65, would would appear a more favourable choice for leader.
Najib's's accommodative style of leadership has seen him more willing to accede not only to communal demands such as the expansion of vernacular education but also - to some extent - in tolerating internal dissent.
In contrast, Muhyiddin is more assertive in his approach, being less willing to concede ground from the status quo even if it means ruffling the feathers of BN partners.
An example was in June when Muhyiddin who is also Education Minister shot down calls to review the status quo on the number of Chinese independent schools despite mounting pressure on MCA from the Chinese community.
However, he backtracked two days later after discussing the matter with Najib and the cabinet.
Najib's tenure has also seen gradual phasing out of ethnocentric policies, such as the liberalisation of industry sub-sectors under the New Economic Model (NEM) and the reduction of bumiputera quota for the Public Service Department scholarships from 90 percent to 60 percent.
For the conservatives in Umno which still comprise the bulk of the party, the encroachment into such quotas is an erosion of Malay dominance.
Najib, 59, has faced unprecedented push backs from within his own ranks and Umno-friendly organisations that traditionally would not publicly hit out at the Umno president.
The Malay Chambers of Commerce Malaysia had flayed Najib for not providing any contracts to its members for the MRT project while right-wing Malay rights group Perkasa had demanded that bumiputera quota for scholarships and economic equity be retained.
While the friction may appear driven by the ambitions of Najib and Muhyiddin for the premiership, it reflects a larger ideological struggle within Umno where both leaders must pander to their respective bases.
Najib who is BN chief and has his political career on the line in the next general election, must appeal to all Malaysians while Muhyiddin who is in a safer position, is more likely to accede to party demands.
Political opponents aware of the precarious balance have attempted to capitalise on this by attempting to further drive a wedge between the duo.
Last week, posters calling for Muhyiddin to be made prime minister before the next general election to "save BN" were distributed at shopping malls in Muhyiddin's home state of Johor.
Johor Umno had since lodged a police report over the matter, claiming it to be an act of sabotage.
Preventing deja vu
In July, Muhyiddin publicly nudged Najib into holding polls this year.
"I don't think the wait will go into next year. However, it depends on the prime minister, but I've told him that this year is the best time (for the general election)," he had told the Batu Umno division at its annual delegates meeting.
Though the deputy prime minister had acknowledged the prerogative remains with premier, the public nudging before Umno grassroots is expected to apply pressure on Najib.
Umno has seen its fair share of friction between its top two leaders which helm the prime ministership and deputy prime ministership.
Mahathir's 22-year tenure saw three deputy prime ministers namely Musa Hitam (left), Ghafar Baba and Anwar Ibrahim being deposed before the reins were handed over to former premier Abdullah Ahmad Badawi.
In 2009, it was Abdullah who became a casualty when he led BN to its worst performance in the 2008 general election. The attack to unseat him was not led by his then deputy Najib, but by Muhyiddin who was at that time trade minister.
Mindful that this could happen again, Najib has refused to rush the polls, meticulously setting the stage for the next general election as failing to outperform Abdullah might mean suffering the same fate as his predecessor.