Unless something very strange happens, Trump is roughly 75%+ to win the nom based on historical data (see 538). If anything, his position has strengthened over the past few months as Death Santis faded hard into a multi-way tie for second place.
Biden obviously faces headwinds, real and imagined but the sad thing is that many voters are utterly delusional about reality. We still have a 4% unemployment rate at most, and steady GDP growth while many advanced economies are muddling along. The statement that the economy isn't working for average folks is not very accurate, because significant wage growth over the past 5 years has been at the very bottom. Everyone feels the effects of inflation, and I won't dispute that has had a real impact. However household net worth is at an all time high, mainly because housing prices have defied gravity due to lack of inventory. I laugh anytime it's said that the housing market is stuck because too many homeowners are "trapped" into their 3.x% mortgage rates. Who wouldn't want to be in such an unfortunate predicament?

This isn't just the top 2% investor class, as many American families now have a lot of home equity built up. Obviously anybody invested in U.S. equities feels good about the big rally since March 2020.
The L.A. Times reviewed the state of Bidenomics on Friday (sorry about the paywall):
With unemployment at historic lows and economic growth brisk, why do so many people tell pollsters the economy is bad? Is it inflation? Or politics? Biden's future may ride on the answer.
www.latimes.com
Last month, only
16% of U.S. adults said the economy was even “somewhat good,” according to the latest poll for the Associated Press conducted by NORC at the University of Chicago. More than 7 in 10 Americans labeled the economy as some level of poor, with 31% calling it “very poor.”
On balance, this shit just doesn't make any real sense. Obviously everything is tribalism and Trumpism nowadays but nearly the entirety of GOP voters have gone all in on the MAGA cult:
Who are those people? NORC found that 82% of Republicans who call their personal financial situation good view the economy poorly. Only 38% of Democrats with good personal finances say the same.
Certainly there are some other factors contributing to Biden's low approval ratings: the migrant crisis, his age+VP stand out. But if a bunch of people are saying "I'm doing well but the national economy isn't," I don't see how a candidate Newsom or Whitmer is the solution to that problem. And if the economy
actually slows down in 6 months, we're probably sunk.
To some extent, the administration is also a victim of its own success. Its major legislative wins are somewhat longer-term investments and wonkish, and so average folks just don't care. Also, remember everyone was so gung ho about stimmy money in 2020-2021. But once the spigot was shut off, and inflation jumped, people are basically asking "so what have you done for me lately?"
To be clear, I'm as concerned as any person should be about the latest batch of polls. But I also have clear eyes and don't see a slam dunk alternative stashed on the sideline; we can't just check in a Michael Jordan superstar because he doesn't currently exist.