Mr. Espada has said he joined the effort because he wanted to change how Albany does business. Indeed, shortly after taking power on Monday, Republicans enacted new rules for the Senate, including one imposing six-year term limits for the Senate’s leaders and another equalizing distribution of the $85 million the Senate allocates annually for legislative earmarks.

But Mr. Espada was said to have grown frustrated about power and money.

Mr. Espada has been fined more than $60,000 for ignoring state law requiring disclosure of campaign contributions. A nonprofit organization that he ran for decades, Soundview HealthCare Network, is being investigated by the attorney general on suspicion of having misappropriated funds. And the Bronx district attorney is investigating whether he lives in the Bronx district he represents.

After he agreed earlier this year to back Mr. Smith, Mr. Espada requested perks that he believed should accompany his title as vice president of the Senate for urban policy. He asked for the use of the Capitol office adjoining his, close to $100,000 for rent for his district office  more than twice the amount allotted to other senators from New York City  and a dozen extra staff members. Mr. Aponte denied the requests.

Mr. Espada also clashed with Mr. Smith over housing legislation that the Democrats had promised tenant advocates they would pass. For months, Mr. Espada, the chairman of the Housing Committee, had delayed introducing the legislation. Landlords increasingly viewed him as one of their only defenders among the Democrats.

Mr. Espada sought more than $2 million in earmarks this year for two groups with links to Soundview.

State records indicate that the groups were created just days before Mr. Espada put in the requests, which Senate Democrats rejected in early April, saying they could not confirm that the groups were legitimate nonprofit organizations.

For example, Mr. Espada requested $1.3 million in grants for the Bronx Human Services Council Inc., which registered with the state on March 26. The council’s headquarters are at the same Bronx address as a clinic that is part of Soundview. Its chairman is one of Mr. Espada’s Senate staff members.