From the context ( a headline and brief report), I think the implication is that Croatia's "behaviour" leaves one feeling as though one is wading through mud. It's not a term I've seen anywhere else, but it is an expressive one = an immediate image of a wet, muddy dip in the ground.
The headquarters of the US Department of State is in a neighborhood of Washington DC called Foggy Bottom Foggy Bottom - Wikipedia, the free encyclopedia. This might be an intentional play on words by the author who seems to be trying very hard to think of interesting expressions.
soggy bottom 
Linear Mode
