Nick,
Biden's comment likely did minor damage to Harris's chances because he is out of the running and a gaff machine.
The Harris strategy is to make Trump the enemy and NOT his supporters. Biden's unwise comments (and, previously, Hilary Clinton's) reinforce Trump's support.
Hopefully, Harris will win. But moving forward, the Democrats have work cut out for them to attract folk from the MAGA camp into the party. If they fail to do this, another will take up the populist reins of grievance.
That this election is close and dangerous says plenty about the shortcomings of the Democratic Party. This is NOT a time for smugness.
Best.