Sacks, 64, has contributed about $500,000 to mayoral challenger Alexi Giannoulias and backed Common Ground Collective, a political action committee that has opposed Johnson’s proposals and is supporting candidates opposed by the Chicago Teachers Union in the Nov. 3 school board election. The group has also targeted City Council members aligned with the mayor.

The clash reflects a broader contest over who wields influence in Chicago politics: unions and elected officials who describe themselves as defending public education and working-class residents, or wealthy donors who say they are supporting moderate Democrats and the future of city schools.

Sacks and his wife have spent $9.2 million on Illinois Democratic candidates and causes since the beginning of last year, according to campaign records. Sacks also helped raise money for Chicago’s 2024 Democratic National Convention and has long been a major donor and behind-the-scenes adviser to prominent Democrats.

The relationship between Sacks and Johnson was once markedly different. Sacks gave $200,000 to Johnson’s inaugural committee and met with the mayor-elect shortly after his 2023 runoff victory to offer advice on organizing his administration. Johnson later blamed Sacks for helping defeat the mayor’s proposed corporate head tax, an accusation Sacks denied.

The mayor has also connected today’s opposition to Sacks with past decisions under former Mayor Rahm Emanuel, including the closure of 50 public schools in 2013. Johnson has said Sacks’ role in the Emanuel administration makes him accountable for its choices. A mayoral spokesperson said Johnson has been responding to Sacks and Common Ground Collective’s efforts against the city’s progressive movement.

Sacks was a close Emanuel ally and led the city’s public-private economic development agency, World Business Chicago. Emanuel said Sacks advised him on economic development, finance and school funding, while also noting that the two sometimes disagreed. Sacks helped advocate for Illinois’ evidence-based school funding formula, which increased state support for Chicago Public Schools. But the legislation also included the Invest in Kids tax-credit scholarship program, which critics argued diverted resources toward private-school scholarships.

Chicago Teachers Union Vice President Jackson Potter says Sacks’ past ties to Emanuel and current spending make him a legitimate subject of scrutiny. Potter has criticized Sacks’ involvement in school board races, arguing that a wealthy donor who does not send children to CPS should not shape a system governed by Chicago residents.

Sacks says he cares about public education and points to his mother’s work as a CPS teacher. He has also funded college scholarships for 162 CPS students to attend Northwestern University. He describes Common Ground Collective as an effort to elect moderate Democrats and says he is pushing back against attacks on him.

Sacks’ political profile has grown alongside an increasingly bitter dispute with union leaders, particularly CTU President Stacy Davis Gates. Sacks says the conflict deepened in 2024, after Davis Gates accused him on social media of advancing a Trump-aligned agenda. He said he had told her he would support Common Ground Collective and would not be driven out of Democratic politics.

The mayor and union leaders have also tied Sacks to opposition to Johnson’s 2024 City Council resolution calling for a ceasefire in Gaza. Johnson has said he faced political retribution after speaking out about Palestinians. Sacks, a Jewish donor who has contributed to pro-Israel advocacy groups, has accused his critics of antisemitism. Potter and state Sen. Robert Peters, who is Jewish, reject that characterization and say scrutiny of Sacks’ political spending is warranted.

Sacks’ allies point to a record that includes support for gun-violence prevention, reproductive health initiatives and economic development in neighborhoods beyond downtown. Former Cook County State’s Attorney Kim Foxx has said Sacks helped her explain her criminal-justice reform agenda to business leaders and contributed $1.1 million to her 2020 reelection campaign. Chicago Federation of Labor President Bob Reiter also praised Sacks for helping broker a settlement in a hotel workers’ strike.

But as Sacks directs more of his wealth toward elections, his past influence and present political spending have become campaign issues in their own right. The dispute is likely to continue through the school board contests and the 2027 mayoral race, where Johnson and Giannoulias are political rivals and Sacks is now a highly visible participant.