... and why he is "courting" our adversaries and antagonists.
T***p has long been associated with mobsters, having allowed his casinos to launder money for them "back in the day". (For more, just "google" his ties.)
It appears he is using his previous corruption experience and "street smarts" as a "fence" to gain in-roads to, and "handle", foreign leaders.
He acts and looks tough, which mobsters like (and the leaders he is kissing up to are mobsters or gansters, have no doubt). He uses this facade to gain a kind of connection ("he commiserates with them" or "he understands them" or "he's one of them"--"compadre") that he exploits to gain their interest (not trust, because one mobster never trusts another). Then, he insists on meeting, personally, because T***p is absolutely certain in his ability to charm and manipulate.
What does he want in that meeting? Nothing more than to solidify that connection into a kind of "cabal" that is intended on benefitting each in a highly personal way--not for the benefit of any country. Call it a kind of business relationship, with the terms of any deal(s) to be worked out later. They separate with an "understanding" of what each one wants and is willing to give up.
Why be rude to U.S. allies? Simple.
It is intended to prove to (or reassure) the anti-freedom leaders (that he is, or will be, "courting") that he is different from the "goody" U.S. allies. By disrespecting them, deliberately stepping on their prior relationship with the U.S, even threatening the continuity of those relationships, T***p is acting out what he hopes will be signs that what he professed to those leaders is true (mobsters rarely believe in words; actions must do the talking).
Consequences are not given much thought because, first, there is little-to-nothing the allies can do about the changes.
Second, and more significantly, T***p knows, as do all gangsters and mobsters, that "good guys" can be relied upon to "think the best", "toe the line", "play along", "stand to", etc., even in the face of unseemliness, if there is no overt, concerted illegality displayed. They stand with, and by, the law.
So, any rude treatment by T***p will be "overlooked as due to ignorance" or "dismissed as temporary" or, possibly, even "forgiven as 'a bad day'" ... to a point. T***p toes the line of that point, even testing it, but he will not consciously step over that line.
What is T***p's end game?
Unclear, although, it is fair to say that ...
---people who distrust T***p will believe it to be destructive, self-serving and harmful to the U.S., while
---people who "like" T***p may believe it could result in an overall benefit, even if also self-serving.
Looking at his conduct from a business perspective, decades ago, rivals in many selected business industries "conspired" to make huge "trusts" in order to reduce competition and drive up profits, eliminate unions and keep workers at minimum wage (monopolies). Eventually, they were "busted up" by law enforcement acting under the anti-trust/anti-monopoly laws.
T***p may be looking to renew the idea of "trusts", although, again, the ultimate purpose of any trust is unknown, though, traditionally, negative for the ordinary person. There are no laws currently applicable that could prevent this "plan".