Can’t respond with any studies but based on my own experience (and failings), it often begins with a feeling of, “What else have they lied about?” This usually occurs after one starts questioning ‘the system’. At the same time, seeing entities like Russia/China/etc. as the only forces combating whatever represents “the system” for them can contribute to this mindset.

Using the vague “the system” since this pattern of thought isn’t exclusive to any one group, such as tankies, but rather is a more widespread phenomenon.