Independent Democratic Conference

In January 2011, Klein announced that he would lead the newly formed Independent Democratic Conference (IDC), a group of breakaway New York State Senate Democrats.

Following the 2010 census, New York redistricted the Senate, expanding it from 62 to 63 seats as of January 2013. The 34th district of New York Senate where Klein was elected was gerrymandered to combine a majority white district in the Bronx with Jewish neighborhoods in Riverdale and in the East Bronx.^[9] When all election night results were tabulated on November 6, 2012, it appeared that Democrats would hold 33 seats for a three-seat majority, their third Senate majority since World War II. Yet not long after the Senate Democrats' momentous victory, on December 4, 2012, Klein and the Republican Leadership announced a power-sharing agreement between the IDC and the G.O.P. in order to govern the Senate in a bipartisan coalition.^[10] Under their power-sharing arrangement, the IDC and the Senate Republicans jointly controlled the Senate legislative calendar (determining what bills would reach the Senate floor), made assignments to Senate committees, decided appointments to government boards, and negotiated the state budget.^[11] Sens. Klein and Skelos also agreed that the title of Senate President would shift back and forth between the two of them every two weeks.^[11]

Klein was a prime sponsor of the 2013 New York Secure Ammunition and Firearms Enforcement Act (NY SAFE Act), which enacted new comprehensive gun control measures statewide in the wake of the Sandy Hook Elementary School shooting in Newtown, Connecticut, and in response to mass shootings nationwide.^[12]

Klein was the primary sponsor of proposed "At Rest" legislation, which would require liquor sold in New York State to be stored in warehouses located in New York State. Wine retailers, New York wine producers, and smaller wine wholesalers argue that the legislation would drive up the cost of wine and spirits in New York State and significantly benefit large New York State liquor wholesalers such as Empire Merchants, which donated over $53,000 to Klein's campaign between 2009 and 2014.^[13]

Prior to the 2013 state budget negotiations, Klein publicly demanded that New York increase its minimum wage as part of a final agreement.^[14] Klein's support was seen as critical to the measure's success, which will increase New York's minimum wage to $9 per hour by the end of 2015.^[15]

Liberal activists working with the Democratic Party and the Working Families Party targeted Klein in 2014, with Oliver Koppell challenging Klein in a Democratic primary.^[16] Due to pressure from Governor Andrew Cuomo and labor unions, Klein indicated in June 2014 that the IDC would rejoin the Democratic caucus after the November 2014 elections.^[17] Klein defeated Koppell.^[18][19]

In the 2014 general election, Republicans won back the Senate majority.^[20] The election results meant that Klein lost his position as Senate co-leader.^[11][21][22] Though Klein had previously stated that the IDC would rejoin the Senate Democrats, the IDC decided to remain allied with the Republicans in the 2015 legislative session^[21][23] despite their conference's diminished role.^[11]

Klein was a partner in the law firm Klein, Calderoni & Santucci, LLP, but divested from the law practice in 2015 and continued to call for lawmakers to give up their outside income.^[24]

Klein and his IDC colleagues rejoined the Senate Democratic Conference in April 2018 at the request of Gov. Andrew Cuomo.^[5][4] At that time, Klein was appointed to his former role as Deputy Democratic Conference Leader.^[1]

Sexual harassment allegation

In January 2018, Klein was accused by a female former staffer of having forcibly kissed her in 2015. Klein denied the accusation.^[25] Despite the allegations, Klein took part in high-level negotiations regarding sexual harassment legislation in 2018.^[26] The New York Joint Commission on Public Ethics opened an investigation into the allegation, though by the time it went to an administrative hearing, Klein was no longer in the State Senate, having lost his campaign for reelection.^[27]

Klein later petitioned to shut the investigation down pointing to findings by the assigned hearing officer, who had encouraged the commission to drop the investigation in June 2020, after concluding that the Public Officers Law under which Klein was charged would not apply because the alleged incident appeared to be isolated and didn’t affect government decision-making. JCOPE, in August 2020, voting 9–2 to proceed with the investigative hearing.^[28] Klein's lawyers attempted to get the lawsuit dismissed in January 2021. Yet, Vladamir and her lawyers and her organization of former ALbany legislative staffers continue to fight for justice.^[29] In March 2023, Klein failed to have the legislative investigation (or probe) into the allegations closed by investigators. The Appellate Division Third Department in Albany ruled against him on March 9, 2023. Klein did not appeal the ruling. He originally requested the investigation into the accusations against himself while he was still a New York State Senator.^[30]

2018 loss to Biaggi

Lawyer and first-time candidate Alessandra Biaggi, 32 years old, challenged Klein, who had held the seat for 14 years, in the 2018 Democratic Primary election.^[31] Klein outspent Biaggi by a rate of 9-to-1, spending $2 million to her $200,000.^[32] Biaggi defeated Klein in the primary in a major upset, 54%-46%.^{[33][6][34][35]} His upset loss was attributed by some to anger with the former members of the Independent Democratic Conference.^[36][37]

As New York's electoral fusion laws allow candidates to appear on multiple ballot lines in an election, Klein still appeared in the November 6, 2018, general election on the third-party Independence Party of New York ballot line.^[38][39] Biaggi defeated Klein again in the general election.^[40]