The largest mobilization in the history of–and in favor of–immigrants stretched for a mind-boggling twenty-six blocks through downtown Los Angeles Saturday, bringing somewhere between a half-million and a million people into the streets.

Politicians, police and even organizers of the pro-immigrant rally were amazed by the massive turnout–five to ten times bigger than the still-talked-about 1994 rally against Prop 187–and surely the biggest political demonstration in LA history.

Labor, religious and civil rights groups worked for months to put this event together, but no one expected such a massive outpouring. "We’re just blown away," one union organizer told The Nation. "This thing just snowballed on its own and became humongous."

The LA demonstration and rally is one of a series of nationwide events timed to coincide with the historic Senate debate on comprehensive immigration reform. The big urban demos are being called in the name of repudiating draconian anti-immigrant legislation passed by the House last December. While that measure has little chance of becoming law, the Senate on Monday is scheduled to take up the issue of a guest-worker program that would provide hundreds of thousands of migrants with a legal channel to come to the United States. The Senate is also looking at proposals that would legalize the 12 million undocumented already lving here.

A dozen years ago, when anti-immigrant forces pushed through Prop 187 in California, it provoked a Latino backlash that has created an ongoing disaster for the state GOP.

Are we on the verge of seeing the same thing now on a national scale? While Democrats and liberals have spent oodles of time this year debating everything from Downing Street to impeachment and censure, they have been mostly AWOL on the immigration issue–one that has now brought a million people into the streets in just the last week.

I’ve a longer analysis of Saturday’s march on my blog.

Looking at the eye-popping pictures in Saturday’s LA Times you have to ask yourself if either of the two parties are going to fully "get" this issue. Here’s someone who does.