IMMIGRATION REFORM ADVOCATES HOLD NATIONWIDE RALLIES…. Last weekend, tens of thousands gathered to urge policymakers to approve legislation to combat climate change. This weekend, even larger crowds pointed to the urgent need for immigration reform.

Angered by a controversial Arizona immigration law, tens of thousands of protesters — including 50,000 alone in Los Angeles — rallied in cities nationwide demanding President Barack Obama tackle immigration reform immediately.

“I want to thank the governor of Arizona because she’s awakened a sleeping giant,” said labor organizer John Delgado who attended a rally in New York where authorities estimated 6,500 gathered.

That’s an interesting choice of phrases. I’ve seen the “sleeping giant” idiom used many times of late by conservative Republicans describing far-right activists who turn out to protest their perceived outrages. The point is to suggest that policymakers have a responsibility to heed the concerns of those who get involved, speak out, and appear at large, organized gatherings.

If that’s true, of course, then yesterday’s events — from L.A. to D.C. — deserve ample attention, too.

Estimates vary, but there were reports of crowds of 50,000 in Los Angeles, 10,000 in Chicago, 25,000 in Dallas, and thousands more in D.C., San Francisco, Milwaukee, and elsewhere. Organizers said there were events in more than 70 locations nationwide.

The NYT noted, “The bigger demonstrations were far larger than planners had anticipated in March, when the events were first announced.”

Recent events in Arizona, and the burgeoning debate on Capitol Hill, no doubt helped spur interest.

Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.