"Odinga betrayed us,” Mr Mbowe said.
He commended Mr Kenyatta for “boosting democracy”.
“Opposition leaders in Kenya haven’t been jailed, let alone arrested arbitrarily.”
However, Chadema party leaders did not provide details of the nature of support they would give Mr Kenyatta, if any.
Tanzanian police last year banned political rallies, a move the opposition considers undemocratic and unwarranted.
Two weeks ago, MP Halima Mdee was arrested allegedly for insulting the President after she criticised him for his support for a ban on schoolgirls who get pregnant.
She described him as “problematic” and questioned his competence.
Earlier this month, Foreign Affairs and East African Cooperation Minister Augustine Mahiga denied reports that Tanzania was interfering with the Kenya elections in favour of Mr Odinga.
During the Tanzanian elections in October 2015, Chadema along with other opposition parties – CUF (Civil United Front), NLD (National League for Democracy), and NCCR-Mageuzi formed a loose alliance – Umoja wa Katiba ya Wananchi and fielded Mr Lowassa for the presidency in a contest billed as the closest presidential race in Tanzanian multi-party electoral history. He was beaten by Dr Magufuli.
Like many Socialist societies, Tanzania is a land of many wise men: people who are respected and wield influence in the secret services, army, police and CCM, not because of their official positions, but because of their history in the service of the party and the country.
Some have served in the Central Committee of CCM, one of the most powerful organs in the country.
Many of these informed sources in private believe that Dr Magufuli would have found it extremely difficult to win the election without the support of an IT team that had set up a tallying centre at Double Tree Hotel in Dar es Salaam.
They also believe that Mr Odinga helped Mr Magufuli assemble the team.
The IT team apparently included experts from Germany, Israel, Kenyans and local Tanzanians.
Aside from offering IT expertise, it also offered public information and PR support.
The programme was managed by Mr January Makamba, who was the head of the Magufuli election secretariat and is now minister for Environment.
A source privy to the inner workings of the Magufuli presidential campaign secretariat said the team also consisted of political strategists who shaped Mr Magufuli’s campaigns, especially in crafting key messaging pillars.
The team was in Dar es Salaam between April and September that year.
“A monumental challenge that faced us was first to pocket the CCM nomination, Magufuli was not the one who in English is called a hot favourite,” a Magufuli aide who requested anonymity told the Nation correspondent, and added: “That is when Magufuli asked for assistance.”
On Sunday, Mr Makamba denied the existence of such a tallying centre, saying CMM only had a command centre, just like any political party.
He also said that it would have been illegal for the campaign to accept foreign assistance.
Mr Magufuli surprised many within CCM when he was picked as the compromise candidate.
Mr Lowassa, an earlier front runner, defected to the opposition.
At the Uhuru Stadium in Dar es Salaam during the swearing-in ceremony, President Kenyatta was given a warm but ordinary welcome reserved for leaders in the neighbourhood.
Mr Odinga, on the other hand, “looked very special because of his relationship with the President”, an observer said.
Neither was it lost on political observers that President Magufuli departed from protocol where the hosting president poses for a picture with each visiting Head of State and government.
In the case of Kenya he posed with both Mr Kenyatta and Mr Odinga.