A single poll doesn't tell the whole story. I don't think Trump has broken 43% approval on 538 since his inauguration: https://projects.fivethirtyeight.com/trump-approval-ratings/
His biggest lows were when his antics were still shocking. They've rebounded as they've been normalized. We need to get back to the place where it isn't treated as normal, and the way to do that isn't by treating the deplorables like they are normal, IMO.
RCP current averages of the front-runners:
Biden 49, Trump 41
https://www.realclearpolitics.com/epolls/2020/president/us/general_election_trump_vs_biden-6247.html
Sanders 50, Trump 43
https://www.realclearpolitics.com/epolls/2020/president/us/general_election_trump_vs_sanders-6250.html
Yeah, the next tier is only up about 3 points over Trump, but I don't think that's indicative of Trump having greater appeal than his approval rating reflects. Warren, Kamala, and Pete are taking off right now as the country gets to know them, and that will be reflected in the head-to-heads soon.
I don't dispute that Trump can win. I just think the way to beat him is by focusing on the 57% of voters who already don't approve of him. Energize the left with progressive policies. Attract independents by being stable and sane, and by actually standing for something concrete and aimed at helping people who are struggling. Make it a choice between racism and sociopathy and incompetence, on the one hand, and expertise and sanity and kindness, on the other. That wins more than the 80K votes across the blue wall that made the difference.