Of is being used in one of its regular prepositional meanings.
"criticism of her hair" = saying her hair is bad.
I think this can be analysed as a form of "objective genitive" with a noun indicating an action (criticism = the act of criticising) and the noun functioning as the object using a genitive form (of ...)
So in the example, we have "criticism [...] of [...] Trump's proximity to Putin" = "saying Trump's proximity to Putin is bad".
The criticism is coming from across the Atlantic (ie from critics in America as Trump is currently in Europe)