Irony? The irony is that Barack Obama, as president, likewise reneged on an Executive agreement reached by one of his predecessors. In the 1994 Budapest agreement, Bill Clinton agreed to guarantee Ukrainian territorial integrity in return for Ukraine, which had inherited a huge nuclear arsenal following the collapse of the USSR, turning over those weapons to Russia. There was no formal treaty approved by the Senate. The accord was an executive agreement. And when Russia occupied the Crimea, then a recognized part of Ukraine, what did President Obama’s do? Sanctions! I’m certain that if Bill Clinton had promised the Ukrainians that if Russia grabbed a chunk of their territory he would hit them with sanctions, they would have told him to get lost and trusted their nuclear arsenal to deter Russia.
Obama had the option to offer JCPOA as a treaty to the Senate. But he knew he’d NEVER get the deal ratified. So he went the Executive agreement route, one he had himself so recently undermined, and set the stage for Trump’s reversal.