It was a scene that immediately put every American into one of two groups: those heartened by the throngs of illegal immigrants thirsting to stay in this country, and those appalled. It also framed a choice for voters, because the crowd was responding to a decision by President Barack Obama to stop deporting some foreigners who arrived without benefit of the law.
It's not really accurate to call them foreigners, though. These are young people who were brought here when they were still children. Many arrived as infants or toddlers; many speak English like natives; and many have no memory of their birth country. Everything about them says "American" except their birth certificates.
For years, they've had to live with the possibility of being caught by immigration agents and evicted from the only home they know. But in June, Obama announced the administration would stop removing those who meet certain criteria.
The exemption would cover those under age 31 who came before age 16, have lived here five years or more, are attending school or have graduated from high school or have served in the military, and have no serious criminal record.
The reprieve would last two years -- or, possibly, until Mitt Romney moves into the White House. Republicans in Congress denounced the change, and their prospective nominee says, "I will build my own long-term solution that will replace and supersede the president's temporary measure."
The change does more than lift the threat of being deported. It also lets those affected work legally, qualify for college financial aid and get driver's licenses. Unlike the farsighted Dream Act, which Congress spurned, it doesn't provide them a path to citizenship or any permanent immunity.
Critics say Obama has brazenly usurped the authority of the legislative branch by implementing something he couldn't get lawmakers to pass. But the executive has long exercised discretion over which illegal immigrants to banish and which to keep. Utah's Republican Attorney General Mark Shurtleff supports Romney but says, "This is clearly within the president's power."
John Lennon, who should not have been allowed in because of a drug conviction, was in line to be deported in the early 1970s until his lawyer got the immigration agency to classify him a "non-priority," allowing him to stay until his death in 1980.
Margaret Stock, an immigration attorney in Anchorage, Alaska, tells me that deportable foreigners have long been eligible for "deferred action status." She has sought it for many clients and says, "Previously it was really the whim of the local office whether you got it or not."
Until now, she says that "it was pretty much one of those things that lawyers knew about but the general public didn't." The Obama administration has merely extended to a large, well-defined group an option that used to be available mainly to a few with the cash and savvy to hire a lawyer. British pop icons? Sure. Mexican janitors? Probably not.
Republicans say Obama's policy rewards people for breaking the law. But the young people affected by the change had no say in the decision. Banishing those who grew up here because of what their parents did punishes the innocent, not the guilty.
The other complaint is that the policy will force Americans to compete for jobs and college admission with those allowed to stay. But immigrants, legal or illegal, not only fill jobs but create them. Historically, there is no correlation between higher immigration and higher unemployment.
And if foreign-born students have done everything to qualify for higher education, why shouldn't they be allowed to pursue it on the same terms as their peers? What the 13,000 people who showed up at Navy Pier want is what conservatives are fond of promising: not a guarantee of success, but an opportunity to make the most of their abilities.
It's a dream that is American to the core. No one should be surprised that on Wednesday, they interrupted the proceedings to recite the Pledge of Allegiance.