For the second time in two weeks an American city was rocked Sunday by a pro-immigrant demonstration of undeniably historic magnitude. As many as a half-million people, wearing white and waving American flags crammed downtown Dallas. A similar, but smaller, outpouring took place in nearby Forth Worth. Scores of thousands of others also came into the streets in Salt Lake City, Miami, St. Paul, Des Moines, Boise, Salem, Detroit and San Diego (with one report saying the crowd neared 100,000 in the latter city).

The Dallas demonstration –- which mushroomed to ten times the size anticipated by authorities — rivaled the scope of the so-called "Gran Marcha" in Los Angeles two weeks ago – an event that to many observers marked the birth of a new civil rights movement. The L.A. demo was also the largest in the history of the city — perhaps in all of the western United States.

And on Monday even more massive pro-immigration demonstrations are scheduled for 140 more American cities in a national day of protest. Once again Los Angeles is predicted to be the epicenter of the day’s activities. As many as a quarter million of a people are expected there as well as an equal number in New York and Washington DC– perhaps a total of two million or more nationwide.

The demonstrators are protesting a draconian enforcement measure approved last December by the House and are instead calling for liberalized reform, which would legalize migrants already working in the U.S. and provide expanded channels for future legal immigration.

"It is the largest national mobilization of immigrants in the history of this country," Juan Carlos Ruiz, coordinator of the National Capital Immigrant Coalition, the umbrella group organizing the event in Washington told the Los Angeles Times. "The goal is to show Congress and the media and the White House that we can organize ourselves, because we have not been very well organized in the past."

The protests come just days after the US Senate failed to vote on compromise legislation that would have allowed a majority of the 12 million "illegals" already living in the US to come out of the shadows and normalize their status. Though a bi-partisan coalition of more than 60 Senators supported the measure, partisan political jockeying torpedoed the vote. Senate Judiciary Committee Chair Arlen Specter (R-Penn) and Massachusetts Democrat Ted Kennedy have both vowed that after the current two-week recess the Senate will come back and pass a similar measure. Kennedy is scheduled to be among the speakers at Monday’s rally in Washington DC

At the same time, however, the Republican leadership in the House is still promising to block any guest worker or legalization program.

Meanwhile, both parties are no doubt closely watching the movement burgeoning before their eyes. And many observers are predicting that the startling outbreak of nationwide street rallies will pressure Congress toward reaching some landmark legislation sooner rather than later. Neither party has any significant influence over the course of the demonstrations.

Sunday and Monday’s protests have been organized by a broad coalition of interests – ranging from Latino rights organizations, the Catholic Church and Latino-dominated unions including the Service Employees International Union and HERE-UNITE (representing hotel, restaurant and clothing workers). Spanish-language media are acting as lubricants to the protests, rallying their readers and listeners to the cause.

While the overwhelming majority of demonstrators are Latinos, there has also been a significant presence of Asian immigrants. One out of four Korean immigrants in the U.S. lack proper legal status. And news reports say that hundreds of Koreans are planning to attend Monday’s demonstration on the capitol mall.

During one of Sunday’s protests, demonstrators in Birmingham, Alabama trekked along the same route used by civil rights activists in the 1960’s and rallied at a park featuring a statue of Martin Luther King Jr. "We’ve got to get back in touch with the Statue of Liberty," said the Rev. Lawton Higgs, a United Methodist pastor and activist. "We’ve got to get back in touch with the civil rights movement, because that’s what this is about."