The underlying idea here is that apparently a President can't President without doing crimes. That government is inherently criminal. Anarchists would agree. But its hardly a position you'd expect from self-proclaimed "conservatives" (until you remember that the essence of conservativism is hierarchy and unaccountable power - "laws that protect but do not bind"). The Supreme Court may also have sold it to themselves as protecting past presidents from legal persecution by their successors. But with this ruling, a president doesn't need to prosecute their predecessors. They can simply have them murdered instead.
While the ruling permits Biden to order the immediate murder of Trump - or of the Republican majority on the Supreme Court - I don't for a moment expect that to happen. Like most elected politicians in other democratic states, Biden seems to be a relatively normal, non-murdery person, who sees the criminal law as a proper constraint on power, rather than as some obstacle, and his voters would never support such action even if he did. Instead, this ruling effectively authorises a future criminal president - Donald Trump, if he wins or seizes power after November, or the president after him, or the one after them - to act on their worst impulses, without constraint. And given the ideology of violence and power floating around on the American right at the moment, those impulses look like they will be very ugly indeed.
If allowed to stand this ruling effectively signals the end of the rule of law and of democracy in America. Unfortunately Biden's post-ruling speech gives no confidence he will try to build a movement to overturn it.