The “full support” of the US government would do Britain very little good. The problem is of their own making in every sense. It now comes from within. This is not like WW I or WW II where overt US support was critical for Britain’s survival. TodY Britain is akin to a debilitated patient with a lethal metastatic cancer throughout its body. The US “full support” is like an old friend offering to do “whatever he can” for an old, barely recognized friend. It also underscores the futility of modern NATO.
Trump put the ball in Britain’s court. What happens now is up to Britain. Not even the US can fix what refuses to be fixed.