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Some people have suggested that this may be at least partially driven by Republicans who are favorable toward Biden choosing not to call themselves Republicans any more, as they see the party drifting further to the right. I think the opposite is happening, actually. Some data: https://twitter.com/TheEconomist/status/1361872840014913538
Sample sizes for some of these groups are small, so be wary of trying to infer too much, but our Economist/YouGov data suggest show that the Republicans who are favorable to Trump / disapprove of Biden might be the ones who have left; see the big increase in Trump-voting Indies.
If Trump voters are mad at the party leadership who voted to convict Trump and are shirking the party label — as the embrace of Trump's calls for a Patriot Party would suggest — then we would expect GOP opinion toward Biden to get _warmer_, not colder.
So, if anything, I think the polarization in Biden's approval ratings could be worse in reality than we're picking up in survey data. In other words, our increasing divides are not a product of weird anomalies in polling.
1 more thing 2 note: people who called themselves Republicans n January (a smaller group than those that called themselves Rep in Nov) also became less "strongly favorable" toward Trump after 1/6 (see chart). So I think we can be reasonably confident that the leavers are Trumpers
