What rights does a public official have to speak out in the workplace?

Though it is well established that "the government as employer . . . has far broader powers than does the government as sovereign," Waters v. Churchill, 511 U.S. 661, 671 (1994) (plurality op.), it is equally well established that "a citizen who works for the government is nonetheless a citizen," whose rights do not simply vanish in the workplace. Garcetti, 547 U.S. at 419. Thus, when public employees speak "as citizens about matters of public concern," they may be subjected "only [to] those speech restrictions that are necessary for their employers to operate efficiently and effectively." Id.