I feel like I may be insulting your intelligence with how obvious this is, but the Israeli government has had turning Iran into a failed state as an open policy objective since the 1980s. Given that Israeli interests have achieved this end in basically every non-monarchy in the region, I think this is a credible threat. Israel has a highly aggressive and influential lobby in the United States, which has posed debilitating sanctions on Iran for many years now. I’m not saying the religious leadership in Iran are the good guys, but the siege mentality is hardly irrational.