The concept of "nuclear sharing" has been contentious ever since the formation of the NPT.
In my opinion it is an example of following the letter of the treaty while at the same time deliberately violating the intent of the treaty.
It is the position of the United States that if a state of war comes to be, the NPT is immediately invalidated so there could not be any violation in times of war. So our nuclear sharing program is simply preparing for the time when the NPT becomes void.
The following is an interesting article discussing how the concept of nuclear sharing was introduced in the deliberations and negotiations of the NPT.
https://web.archive.org/web/20150128...n-Donnelly.htm