Vigano's words are better late than never I suppose.
Those who are hostile to +Vigano have mis-analyzed his previous statements about Trump as being categorical endorsements. If you read them carefully, he makes statements like, "we dare hope" that Trump is on the side of good (obviously where it comes to natural law, etc.)
Nowhere did +Vigano categorically endorse Trump. Instead, he was trying to appeal to Trump's (massive or yuge) ego to persuade him to take the right side on some issues. +Vigano was a trained diplomat, and he was well aware of Trump's personality. After Trump was snubbed by the commie pseudo-bishop Wilton Gregory for visiting a Catholic shrine, +Vigano wrote the letter appealing to Trump. +Vigano knows that Trump has a yuge but very fragile ego, and that if he's publicly snubbed or criticized, he takes it personally and digs in his heels against them. So he realized that Gregory's nonsense would make Trump hostile to the interests of the Catholic Church. So he knew that praising Trump (even if it was a guarded and conditional praise) would appeal to Trump's ego, making him more inclined to follow through on the questions that +Vigano was exhorting him about. And it worked as expected, with Trump retweeting the latter from +Vigano and being all proud of it.
Of course, Trump's support for sodomy is nothing new. Many of us refused to vote for him in 2020 precisely because Trump had bragged about being the most pro-sodomite President in history. It's possible that +Vigano wasn't aware of some of those prior statements or else passed over them because they were less widely reported or known (the Democratic media hardly would cover something that they felt would help Trump with independent voters).
+Vigano's approach to Trump was taken for prudential considerations. Let's say you have a child who has some good tendencies but also does some bad things. Perhaps you know the temperament of this child, and realize that if you crack down on him for the bad things he's doing, due to a stubborn nature, he would dig in and do them with even more zeal. So you might adopt the tactic of focusing on and encouraging the good things he's going, hoping that those will eventually lead him away from the bad stuff over time.
St. Thomas' teaching about the obligation to rebuke the sinner is quite clear. If you feel that the rebuke would do no good, you are not obliged to rebuke the sinner. In fact, St. Thomas even says that if you believe that the rebuke would cause the person to dig in and even to continue committing the sins with greater zeal, then you may even be obliged NOT to rebuke the sinner. This is where Prudence comes in as the queen of all the virtues. Prudence realizes that the ultimate aim of rebuking the sinner is for the sinner to amend. So then Prudence can determine that in some cases an actual rebuke might work CONTRARY to the ultimate aim, where the sinner might become even less likely to amend. Trump is precisely this child-like type of character. If you rebuke him and offend his ego, he will in fact lash out, dig in his heels, and become even more stubborn about that for which he was rebuked.