AP

The event resembled something between a family festival — with food vendors pushing carts through the grass — and a political demonstration with protesters chanting "Si se puede," Spanish for "Yes we can." A group of undocumented students stood on a stage at the Chicago park and "came out" regarding their immigration status.

Juan Baca was among those students. Baca, 19, whose parents brought him from Mexico illegally when he was 4 months old, said he has had to drop out of college and work several times already because he can't qualify for financial aid.

"It's been a struggle," he said. "I missed the mark by four months. A lot of times you feel like you're not good enough."

Obama once promised to tackle immigration reform in his first 100 days, but has pushed back that timetable several times. He said this week that Congress may lack the "appetite" to take on immigration after going through a tough legislative year. However, Obama and Congress could address related issues, like boosting personnel and resources for border security, in spending bills this year.

"Obama promised legalization in the first 100 days," said Jesus Garzas, a 43-year-old Chicagoan with legal status who wore an Obama mask with a Pinocchio-like nose. "He lied."

Juan Haro, 80, was born and raised in Denver, where about 3,000 people rallied. He said his family is originally from Mexico and thinks Arizona's new law is targeting Mexicans specifically.

"This country doesn't seem to be anti-immigrant," he said. "It seems to be anti-Mexican."

At the White House, U.S. Rep. Luis Gutierrez, an Illinois Democrat, was arrested with several others in a demonstration of civil disobedience against the Arizona law.

In Dallas, police estimated at least 20,000 attended a Saturday rally.

Among them was Juan Hernandez, the Hispanic outreach coordinator for Sen. John McCain's unsuccessful presidential run. He said Arizona was once considered by those south of the border to be a model state with particularly close ties to Mexico.

"It went beyond what most states do," he said. "Now they are a state that goes beyond what the Constitution says you should do."

About a dozen people at the Dallas event carried signs depicting Brewer as a Nazi and Maricopa County Sheriff Joe Arpaio, known for his tough illegal immigration stance, as a Klansman. Organizers were asking sign holders to discard the placards.

In Ann Arbor, Mich., more than 500 people held a mock graduation ceremony for undocumented immigrant students near the site of Obama's University of Michigan commencement speech.

A smattering of counterprotesters showed up at rallies. In Tucson, Ariz., a few dozen people from the group Arizonans For Immigration Control showed up in support of the new law and Brewer.

May 1, also International Workers Day, is a traditional date for political demonstrations. Immigration advocates latched onto that tradition in 2006, when more than 1 million people across the country — half a million alone in Chicago — protested federal legislation that would have made being an illegal immigrant a felony. That legislation ultimately failed.

At Saturday's rallies, activists from organizations supporting other groups — including Muslims, gays and youth advocacy — marched in support of immigrant rights.

"It affects everyone," said Paulie Sabol, 38, who traveled from Indiana to march in Chicago. His partner is a Mexican immigrant who is a legal resident but doesn't have U.S. citizenship. "I can't sponsor him because same sex marriage isn't recognized in Indiana."