[Ramon de Ramon y Ramon]

Though it is not an example of people protesting against government policies: In the early nineties we experienced a surge in violent xenophobic hate crimes here in Germany. As a reaction a series of mass demonstrations in all major cities throughout Germany were staged and the number of recorded/reported hate crimes did decline significantly afterwards. The theory behind this (alleged) effectiveness went as follows: the right extremist perpetrators of these crimes fancy themselves to act out the will of the "people's silent majority" and the huge turnout for the demonstrations shattered that belief.

Of course, proving cause-effect relations is always an iffy proposition with complex phenomena, especially since media focus and subsequent under/-overreporting does have a serious impact on shaping that perception.