An "informed source" close to Mowjcamp says that the IRGC has existing plans to arrest Mousavi and Karoubi after Quds Day. If true, these plans were made before today's massive showing, so the regime would have to recalculate its estimate of public backlash against such a move.
On a somewhat related note, former President Mohammad Khatami was attacked today by security forces a group associted with the Kayhan hardline newspaper:
Masoud Shafaee is an attorney and freelance Middle East analyst based in Washington, D.C. He holds a Juris Doctor from American University's Washington College of Law and a master's degree in international affairs from the School of International Service. He was born in Tehran and hails from California.