A new rule being added that prevents the Death Note being sold on the threat of death of the parties involved comes out of nowhere, resulting in Minoru's death. The number one thing to not do with death is cheating it in any form, which is what Minoru was doing by selling it without using it himself to prevent his life from being taken. Of course the Shinigami would add a new rule to prevent that.
Even though Minoru's plan may have successfully kept the Death Note out of dangerous hands, it might have caused more damage than if he had just kept it to himself. Even with Donald Trump refusing to take the death note, the fact that the public at least believes it's owned by the US government is enough for paranoia and conspiracy theories to inevitably set in as soon as the death of a prominent person in government makes the news, especially with the Reality Subtext of Trump being the President and how little the public trusts him.
It actually gets worse for Trump when you remember that death notes fall out of the sky like raindrops. All it would take is for a bored shinigami you throw their notebook into the human world over the USA and from that there are at least five likely scenarios for how it plays out:
1). The US-Kira is a dyed in the wool Trump supporter. Once they find out about the new rule they will rationalize that A-Kira welched on the sale and that the death note coming into their possession is a sign from God that it's their sacred duty to eliminate Trump's enemies. And once all the big name Democrats and Trump critics start dropping dead, it won't take too long for the blame to fall on Trump.
2). US-Kira is a run-of-the-mill Republican who, in all likelihood, only voted for Trump out of loyalty to the party. After learning of the new rule and that Trump doesn't have a death note, they decide to keep quiet since his stunt has been good for the Republican Party. But again, this loyalty only lasts as long as Trump benefits the Republicans. As soon as Trump stops being useful...
3). US-Kira is a Democrat and a particularly average one at that. After finding out about the new rule l, they'd likely go to whatever news media would have them on to expose Trump's lie. Regardless of how it plays out, it would definitely become the media circus of the year.
4). US-Kira is a far-left radical. After learning about the new rule there's a number of different things US-Kira could do, including framing Trump for murder by using the notebook to kill Trump's political enemies (not unlike the first scenario) in a mad gambit to either get Trump thrown in jail or have him confess to not having the death note at all.
5). US-Kira is an Ax-CrazyOmnicidal Maniac regardless of political affiliation. They could easily frame Trump for killing another world leader and provoke nuclear armageddon. Due to this, the actual best case scenario would be for Trump's lie to be exposed so that any future use of the Death Note doesn't result in global conflict.
Imagine you're Minoru for a minute. Your mom informs you that the US is giving everyone in Japan with a Yotsuba bank account one billion yen each. You can withdraw some of it in a month. A month passes, and as soon as you make your withdrawal, you die of a heart attack. You have a few seconds of consciousness before falling over dead without the slightest idea why.
