Harris.
I think it's going to be very difficult for Republicans to replicate Trump's midwest strength, and Haley is definitely not the candidate to be able to do that.
Other than in OH/IA, Trump midwest strength wasn't that much better than George W Bush . Its Obama's performances there which were the exception where in 2008 he literally had the best performances in WI/MI/PA than any Dem has since 1964 and in 2012 the autobailout/the tea party moving the gop way right on economics allowed him to do really well again.
The problem is that was the exception not Trump's performances in the Midwest. Just look at Bush 2004 vs Trump 2020 in MN/WI/MI/PA
MN:2004: Kerry wins its by 3.5 points
2020: Biden wins it by 7.1 points
WI:2004: Kerry wins it by 0.4 points
2020: Biden wins it by 0.6 points
MI:2004: Kerry wins it by 3.4 points
2020: Biden wins it by 2.8 points
PA:2004: Kerry wins it by 2.5 ponts
2020: Biden wins it by 1.2 points
Remember though in many midwestern cities the population has actually dropped, like in Detriot which is a huge reason why these states have trended Republican since 2004 .