Polls underestimated support for Trump both in 2016 and 2020, so the latest results in key battleground states are very positive for the Republican ticket. Compared to previous cycles, this is Trump's best chance to win by a landslide — and even to secure the popular vote.
Given that polls have shown Harris consistently ahead of Trump, Republicans have resorted to the fact that support for Trump was underestimated in the previous election cycles. One should not expect them to be inaccurate again, though, as pollsters have worked to improve their methodologies.