well i watched Bush and Marsharif in their news conferrence live. Bush said the first he had heard of the threat was when he heard it on the news. Marsharif said "you'll have to read the book". That's all they would say on the matter.
I would guess that the CIA and others probably told masharif in no uncertain terms, side with us or lose everything. And his nuke facilities would have been the first things targeted. And we would have let India walk right through them. A strong India keeps pakistan in check more than anything.
I think it was said by someone. And implied by someone high up.