I think these are two different sets of voters though:
The undecideds that are now swinging to Harris are NOT the voters that swung to Trump in 2016.
The 2016 voters hated Hillary to begin with, were upset with the "status quo" or were looking for a "drastic change candidate" (which would have been Trump or Bernie Sanders in 2016), and were midwestern Blue Collars for the most part.
These are NOT the 2024 undecideds. 2024 Undecideds are Dem liberals and/or Dem youngsters that didn't want Biden. But DO want Harris.
You aren't shaking these voters loose from supporting Harris.
Trump's only (current) hope is to try to convince independents and suburban moms to FEAR POC more than they fear fascism.
IMO.
And I don't believe that will work, either. No matter what he or the GOP come up with to try and slam Harris. Mostly because they have zero vision for the future of America except Fascism, Violence, The Handmaid's Tale, and Tax Cuts for the Top 1% (and **** the Middle Class). Not an enticing future... methinks.