1) If the President did say that word, he said so in a private, behind-closed-doors conversation. He did not say it in public; or in an interview; or in a speech; or in a statement; nor did he have one of his spokespeople say it or release it. In other words, it was private. We are willing to bet the rent money that he is not the first US President to use nasty language or express disturbing opinions in private. Furthermore, we are willing to double that bet, and say that Senator Durbin, the presumptive leaker, has spoken words of comparable value in private, and probably also has heard them spoken by any or all of the last four US Presidents (or presidential candidates) with whom he has held private meetings over the years. Now, if the Senator would disclose all other instances in which Presidents used scatalogical language, or made insulting remarks about people or places, we can compare them to what has just been disclosed and determine the scale of offenses.
2) Of course, the real point is this: any country that is a "mess" is one not because of the failings of its citizens but because of the failings of its government, and most, if not all, of the countries whence America's illegal immigrants originate have governments that are corrupt, dishonest, dictatorial, violent; are places where elections are not free, judiciaries are not independent, the press is controlled, and where kleptocracy and crony capitalism benefit the friends and families of the well-connected while everyone else grubs for scraps. Those places do not to have Constitutional protections or Bills of Rights that are enforced or respected. This is how a nation becomes a disaster. This is how Venezuela and Cuba, for example, went from rich nations to poor ones - not because of the failings of their people, but because of the failings of their governments. "Mess" is perhaps too mild a term to describe them.
3) The most ironic part of this affair is that the people who advocate the loudest for the permanent inclusion of illegal immigrants in America are the ones who are screaming the loudest over the use of the "mess" term. We are not smart enough to figure out how a) those places are so bad that their people must leave them and come here, and are so bad that they should not be sent back to them, but b) one dare not call those places a bad name. Maybe Senator Durbin can explain it.
This all would have been a different kettle of fish (if we can mix our metaphors a bit) had the President said "hell-hole" instead. President Trump, even if he didn't say it, should apologize; and should, we hope, learn this lesson: there is a standard for what HE can say behind closed doors, and for what everyone else can say, and he should be much more careful about what he says and who hears him say it.