"At first the London Press editorialized on Bulgaria according to political party preferences. MacGahan's telegrams reached London at the end of the first week in August and shortly thereafter Baring's "preliminary" report was read by Bourke in Parliament. This was soon followed by publicaitoin of Schuyler's preliminary report. These seemed to confirm the atrocities and the Conservative Press now joined the editorial bandwagon of invective and censure, though it still referred to exaggeration in the reports of atrocities."

Source: Millman, Richard. Britain and the Eastern Question. 1875-1878. Oxford: Clarendon Press, 1979, pp. 177-178.

Sorry, for the long context, but I thought it to be necessary. I need the meaning of bandwagon in this context. I have a vague understanding of what it means, also in this context, but I would like to have a concrete word for it.
It must be somewhat metaphorical.

Thanks for help.