Mike Doran and Tony Badran offer up a predictable rationalization of the president’s piece of pro-Saudi propaganda:
But Mr. Trump understands the centrality of Riyadh in the effort to counter a rising Iran and he is rightly unwilling to allow the murder of Mr. Khashoggi to imperil that strategy.
To call Trump’s Iran obsession a “strategy” is already far too generous, but this does sum up the ends-justify-the-means reasoning behind the administration’s indefensible embrace of the Saudis and their allies throughout the region. Trump shrugs every off Saudi crime and blunder because it supposedly serves a greater goal of combating Iran, and yet each time the U.S. looks the other way or assists the Saudis in their wrongdoing (as we continue to do in Yemen) it makes things easier for Iran’s government. The Khashoggi murder by itself is an awful crime in itself, but it is because it forms part of a pattern of reckless, monstrous behavior on the part of the Saudi government that it has had such a powerful effect on the way many people in the U.S. and the West view the Saudi government and the crown prince in particular. It is that pattern of behavior that proves how useless the Saudis have become to “the effort to counter a rising Iran,” and it makes the administration’s continued support for the kingdom and for Mohammed bin Salman seem even more obnoxious than it already would.
Yemen receives only one mention in Doran and Badran’s piece, and they have nothing to say about the president’s lies about the war or the Saudi coalition’s responsibility for creating famine conditions throughout much of the country. Only professional Iran hawks are foolish enough to buy into the idea that Yemen could become a “base” for Iran, and that is the only time they see fit to mention the world’s worst humanitarian crisis created by the Saudi coalition with U.S. support. 
The president’s statement was especially destructive because it confirmed that the administration won’t be putting much pressure on the Saudis to end the war, and Trump’s lie that the Saudis would “gladly withdraw” from Yemen will help make it easier for them to keep fighting. The authors assert that presidents “routinely advance useful fictions,” but the only interests served by the fiction that Iran is responsible for the war on Yemen are those of the Saudi and Emirati governments and their hirelings here in the U.S. It isn’t “useful” for ending the war in Yemen to lie about who started it, and covering for the Saudis and Emiratis isn’t “useful” for combating what could end up being one of the worst modern famines. Lying about the causes of the war on Yemen is useful only to those that want the war to continue at the expense of millions of innocent lives.

https://www.theamericanconservative.com/larison/the-iran-obsession-and-useful-fictions/