Robert Tracinski explains in a column for The Federalist website why Chicago Mayor Rahm Emanuel shouldn’t be the only one worrying about his failure to avoid a runoff in his re-election bid.

So what went wrong? Emanuel was blindsided by a rebellion from his left. Emanuel had earlier opposed the city’s teachers’ union in contract negotiations, so he was expecting a mayoral challenge from the head of that union, Karen Lewis. When she had to bow out because of health problems, Emanuel assumed the field was clear. But then Jesus “Chuy” Garcia emerged from the Cook County Board of Commissioners and unexpectedly received 34% of the vote to Emanuel’s 45%. They will now face off in a head-to-head race.

What is important is that Garcia is challenging Emanuel from the far left: his mentor, the late Rudy Lozano, was connected to the Communist Party, and Garcia ran by denouncing Emanuel as a member of the “Corporate Wing of the Democratic Party.”

In short, this is a rebellion of the radical “progressive” left against the “neoliberal” moderates: Democrats who at some point have compromised with elements of business and markets, described as “politicians who are socially liberal, fiscally conservative, and more reliant on the support of affluent professionals than organized labor.”

Which is to say: the wing of the party associated with Bill and Hillary Clinton.

Bill Clinton famously campaigned in 1992 as a “New Democrat” pursuing a “Third Way” in which free markets were not always the enemy and “the era of Big Government is over.” This supposed overhaul of the Democratic Party was always more hype than reality—the Clintons’ first priority in office was an attempted takeover of health care—but it did achieve some concrete results, such as a welfare reform. Many on the left have never forgiven the Clintons for this, which is how an inexperienced upstart like Barack Obama could overthrow the Clinton machine in 2008 by billing himself as a true believer and denigrating Hillary Clinton as a cynical compromiser.