Forty-seven Republican senators signed a letter putting Iran on notice that they will not consider themselves bound by any agreement it makes with the Obama administration: ”The next president could revoke such an executive agreement with the stroke of a pen and future Congresses could modify the terms of the agreement at any time.” Liberals are arguing that the senators have crossed a line of propriety by trying to undermine the president’s ability to conduct foreign policy. Byron York is the first conservative I have seen express sympathy with this criticism.