"We have Wamunyinyi who is mature for the post and well poised to keep Governor Kenneth Lusaka's administration in check and ensure Bungoma gets its rightful share from the national government," said Simiyu.
The DAP-K secretary general said the former Kanduyi MP will add to the Azimio numbers in the Senate if elected and help oversight President William Ruto's government.
Speaking at the party offices in Bungoma town on Saturday, Simiyu urged residents to rally behind Wamunyinyi.
"Look, Bungoma county has already spent Sh102 million to renovate offices because we don't have proper oversight as Senator Moses Wetang'ula left the void to be Speaker of the National Assembly, that can only be tackled with Wamunyinyi," he said.
The former Kimilili MP claimed that the Kenya Kwanza government was creating 'dubious' taxes like that on freehold land title holders which needed fierce defenders of the people like Wamunyinyi to oppose.
In what appeared to be a snide remark aimed at his political nemesis, Wetang'ula who has endorsed his former personal aide Wafula Wakoli for the seat, Simiyu described the Ford Kenya candidate as not mature in politics.
The former MP urged the Independent and Electoral Commission (IEBC) to ensure a free and fair election.
Wamunyinyi is banking on his rich experience as a legislator, liberation champion and defender of sugarcane farmers through the Sugar Bill to win the seat.
"I am offering myself as a serious and senior representative for the senate seat. I have agreed to the endorsement from the people of Bungoma who have been repeatedly petitioning me to go for the seat and also my party members," said Wamunyinyi.
According to Wamunyinyi , the decision by Ford Kenya to endorse Mr Wakoli was tantamount to imposing a leader on the people of Bungoma.
Simiyu said the incarcerated Sirisia MP John Waluke if granted bail, would join the campaign bandwagon to boost the DAP-K leader's chances of clinching the seat.
Mr Waluke is expected in court on November 2, to appeal against his conviction and sentencing for 67 years.
But Wakoli has dismissed his competitors saying he is the best bet to replace Wetang'ula.
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"The people of Bungoma believed in Wetang'ula and that is why they voted for him overwhelmingly. As his long-term personal assistant, I have borrowed much from him that will be of benefit to the masses," he said.
Bungoma Senate race has so far attracted more than 15 aspirants, including businessman Joseph Lendrix Waswa and Jacob Machacha, Rev Herman Kasili, lawyer Erick Nakhurenya and former Bumula MP Mwambu Mabonga, among others.
Mabonga will vie for the seat on UDA ticket.
IEBC gazetted December 8, 2022 as the date for Bungoma Senate by-election.