I don’t know what you mean by “class solidarity,” but it was born in the fires of the 2008/2009 bank bailouts in which millions of ordinary people were wiped out financially while the financial institutions were given trillions of dollars. There was a lot of anger at the perception of crony capitalism and elites. The movement itself was grassroots and clearly feared by the powerful. You might not like the goals of the movement, but their anger was palpable, and at one point, something like 10% of the country identified with the movement. There was no way the rich and powerful could let ordinary citizens form such a powerful voting bloc.