Mr. Trump helpfully pointed out another flaw: a president can pardon whoever they want, including themselves. So it's apparently legal for Mr. Biden to send a team to assassinate all his political rivals and then just pardon them.
The Pardon of President Nixon: Annotated
https://daily.jstor.org/the-pardon-of-president-nixon-annota...
> Nixon had considered pardoning himself while in office[0], and sought a legal opinion considering the constitutionality of doing so (his lawyers believed that it was constitutional). However, three days before his resignation, the Justice Department issued its own opinion to the contrary: “Under the fundamental rule that no one may be a judge in his own case, the President cannot pardon himself.”[1]
[0] Pardon Me?: The Constitutional Case against Presidential Self-Pardons
https://www.jstor.org/stable/797310
[1] https://www.justice.gov/sites/default/files/olc/opinions/197...
In the context of Trump:
Explaining the presidential self-pardon debate
https://constitutioncenter.org/blog/explaining-the-president...
> On Monday, June 4, 2018, President Donald Trump said on Twitter that, “As has been stated by numerous legal scholars, I have the absolute right to PARDON myself, but why would I do that when I have done nothing wrong?”[2] His comments echoed those made by Rudy Giuliani, his attorney, on Sunday.
> Here is a brief explanation of the President’s clemency powers, some past cases, and a theoretical look at a Nixon-era question: Can a President pardon himself or herself?
[2] https://twitter.com/realDonaldTrump/status/10036162109221478...
https://www.justice.gov/sites/default/files/olc/opinions/197...
I elaborate on this in a reply to your interlocutor downthread:
What do you think a defense against this would even look like? To attempt to do so sounds almost absurd because it’s just such a remote possibility.
Stronger constitutional limits. For example, pardons should not be a thing that could be done unilaterally. Ideally, they shouldn't be a thing at all.
At the same time, the Constitution needs to be a bit more malleable. The Amendment process is notoriously hard, and the US Senate structure is uniquely unamendable.