It's not unexpected. In the US, a presidential midterm slump is one of the most regular features of the electoral cycle. Labour has also made some very unpopular decisions in response to the Covid pandemic and faces a formidable grassroots campaign against reforms in three waters, health and Auckland's housing.
Labour will be looking forward to the summer hiatus, by which time the precautionary "traffic light" measures will be tested in holding the line against massive and overwhelming outbreak.
There has been much speculation about Collins' leadership but this subsidence in support also lends itself to new, or previously discarded, options pressing forward.
There's still plenty of time before the next election, which must be held no later than January 13, 2024, when the currently elected 53rd Parliament is dissolved or expires.
If the current polling slouch persists, expect to see some familiar or fresh faces popping up. Nature abhors a vacuum, and apathetic voters are prime for turning.