Pundits and politicians who either (1) opposed the Iran nuclear deal at the time and cheered President Donald Trump’s pullout; or (2) opposed the deal at the time, but worried about the impact of a unilateral pullout, can at least agree with those who supported the deal and opposed its abrogation: There is no Plan B.
The last two groups (both of which opposed the pullout, whether they supported the original deal or not) are entitled to point out there is not now, nor was there ever, a backup plan. You can understand their mistrust of those who egged President Trump on, without producing a coherent explanation as to how this would all play out.