Does "pockets" here mean "groups"? I've checked out the unabridged version of Random English Dictionary and found this definition to be close - "any isolated group, area, element, etc., contrasted, as in status or condition, with a surrounding element or group: pockets of resistance; a pocket of poverty in the central city."
I am not very sure.
The shift raises questions about the strength of the support for Mr. Trump and suggests that pockets of his fan base are fracturing. Many of Mr. Trump’s fans still falsely believe he was deprived of office, but other far-right groups such as the Oath Keepers, America First and the Three Percenters have also started criticizing him in private Telegram channels, according to a review of messages.
Source: NYTimes ‘A Total Failure’: The Proud Boys Now Mock Trump