It's called context. Trump was talking about being able to fire people like Lying James Comey and Yarpadarpvich- whoever the Ukraine ambassador was. Although that would be a good start cleaning up the Biden Crime Syndicate.
Someone floated the theory that if Trump paid Ukraine to dig up dirt on Biden, it would be OK. https://dailycaller.com/2020/01/30/hakeem-jeffries-dossier-purchased/
Under Dershowitz's ludicrous theory, Trump could shoot Biden on Fifth Avenue; and claim it was in the national interest, and thereby 'completely legal.'