There are many reasons to pity Melania Trump (although maybe she knew what she was signing up for and got what she deserved – hard to say, really).
Mrs T got into some linguistic hot water with the slogan for her campaign for children’s health and happiness, launched in May 2018: Be Best.
As Tim Hill has pointed out in The Guardian, this doesn’t hold up to what he calls ‘the laws of English grammar’ (I’d soften that a bit and call them rules; English is more flexible than laws would suggest).
One can be good and one can be better, but one really ought to be the best, not just best. That said, it would be idiomatic (and correct) to say It would be best not to do that.
The origin of Melania’s little solecism? Her not always grammatically correct husband, perhaps. Or a desire to outdo, with a superlative, Michele Obama’s exhortation in 2016 for men to be better. Or possibly a staffer’s subtle mockery of the First Lady’s somewhat shaky command of English and its use of definite articles (which are foreign to her native Slovenian).
Not, by any means, the greatest failing of the reign of Trump, but worth noting.