No one knows if the Obama administration will manage in the next five weeks to strike what many in the White House consider the most important foreign policy deal of his presidency: an accord with Iran that would forestall its ability to make a nuclear weapon. But the White House has made one significant decision: If agreement is reached, President Obama will do everything in his power to avoid letting Congress vote on it. Even while negotiators argue over the number of centrifuges Iran would be allowed to spin and where inspectors could roam, the Iranians have signaled that they would accept, at least temporarily, a “suspension” of the stringent sanctions that have drastically cut their oil revenues and terminated their banking relationships with the West, according to American and Iranian officials. The Treasury Department, in a detailed study it declined to make public, has concluded Mr. […]