The immigration rights activists returned to demonstrate outside the Capitol yesterday, as reports of a Senate compromise on an immigration reform continue to seep into media reports.

Most reports put the turnout in the tens of thousands–and noted sympathy rallies in at least 18 states.  Some substantial chunk was turned out by labor unions.  But there were lots of others.  Latino groups were well-represented, and Benjamin Jealous of the NAACP got the most prominent speaking slot.  The Washington Blade trumpeted the participation of gay and lesbian groups at the rally.  Not demonstrating outside, but very much on the minds of members of Congress, was the strong support for reform coming from business interests (Facebook’s Mark Zuckerberg has founded and funded his own pro-immigration group.)

Do the demonstrations outside the Capitol affect the negotiations going on inside?  Sure, but it’s not a simple cause and effect (>200,000 and the waiting period for citizenship drops from 10 years to 8?  Unlikely.).  Rather, Wednesday’s demonstrations are part of a much larger set of campaigns that have pushed immigration reform to the fore, while the results of the last election gave Republicans in particular strong motivation to stand up to the organized and active anti-immigration movement.  Each discrete action is far less important than the much larger effort.

Republican Senator Marco Rubio, a visible player in the Senate negotiations, was well-aware of the political deficits of his party’s posture on immigration and the potential benefits of doing something on the issue.  These demonstrations are a reminder for all concerned.

The activists promise that they’ll be coming back to Washington until substantial reform is passed.  They’ll have to.

Although virtually everyone agrees about the sorry state of the current set of policies, negotiating the details of reform is no easy matter.  Inside the Capitol, legislators are arguing about guest workers, paths to citizenship, and border security.  The demonstrations and the citizen lobbying are efforts to stiffen the spine of would-be allies in negotiations, and big visible demonstrations are likely to yield almost invisible, but still significant, changes around the margins.