Churchill attributed the strength Anglo-American relationship to our shared traditions and ethnic consanguinity.
Now as our populations are changing rapidly on both sides of the Atlantic we are losing both.
It sometimes appears that way but successive generations develop an ability to shift to the center.
In the UK there is a fast change in attitudes among young Muslims for instance. We now have ex-Jihadis writing books about their conversion to British values and the US has been the most successful integrator of Muslims.
Where values can change is if the basic principles become undermined by abandoning for instance the English language as the main language or if the media sways the public to abandon the historic course of the nation in the name of appeasement, or the business ethic falls to corruption.
I would not be so pessimistic. The values of the US and the UK remain virtually the same, polarisation and distortion rise and fall with waves of immigration and events but eventually revert to the center.
It is a historic outcome that both Britain and the US, in pursuit of world goals based on their values, have at times to wield military power; more so currently than any other nations.
However, it only takes one leader or another to break a close bond and the result is that one country or another finds itself alone against the world in a time of crisis.