The IDC has come under criticism in recent days as mainstream Democrats, including Senate Democratic Leader Andrea Stewart-Cousins, blasted the power-sharing coalition for Monday’s failure of the Dream Act and the omission of Democratic priorities such as comprehensive campaign finance reform from the Senate’s proposed budget.

Mr. Koppell previously said if Mr. Klein rejoins mainstream Democrats, the former councilman will not launch a primary challenge. While that condition seems out of the question — with Mr. Klein leading an apparent effort to expand the IDC’s influence in recent weeks — Mr. Koppell has yet to formally announce his candidacy.

“It’s very complimentary to me and I think it’s accurate in its criticism of Senator Klein and his nefarious arrangement with Dean Skelos and the Republicans,” Mr. Koppell said of the petition. Mr. Skelos of Nassau County is the Republican Co-Majority Leader.

“I have not decided whether to run or not, but certainly the petition is an influential factor,” Mr. Koppell continued in a phone interview. “It’s not ultimately the deciding factor, but it’s helpful in moving me toward a candidacy.”

Mr. Klein’s office declined to comment on the pro-Koppell petition. But it pointed to a Change.org petition apparently started by supporters of the incumbent thanking him for his efforts on gun control, increasing the minimum wage and other issues. That document had nearly 300 signatures as of press time.

Testing loyalties

If Mr. Koppell decides to run, his candidacy will severely test loyalties in the northwest Bronx, where both Mr. Klein and his prospective challenger have strong ties.

Mr. Koppell said his connections to the Benjamin Franklin Reform Democratic Club — which has supported him, Mr. Klein and every other successful candidate in the northwest Bronx including Congressman Eliot Engel and Councilman Andrew Cohen — go deeper than those of Mr. Klein. But a key decision maker in the club has declined to declare his loyalties so far.

Assemblyman Jeffrey Dinowitz said he invests little importance in the pro-Koppell petition.