This week brings a constitutional moment illustrating a paradox of Barack Obama’s presidency. The catalyst of the drama is legislation proposed by Sen. Bob Corker, chairman of the Foreign Relations Committee, asserting Congress’ foreign policy responsibilities and prerogatives. The paradox is this:

Obama’s disdain for constitutional etiquette — his contempt for the institutional self-restraint that enables equilibrium under the separation of powers — has been primarily in domestic policy. His anti-constitutional actions have involved the Affordable Care Act, environmental, education, welfare and immigration policies, Internet regulation and judicially rebuked recess appointments, among other matters. Now, however, Congress’ revival comes regarding foreign policy, where constitutional logic and historical precedents are most supportive of presidential discretion.

Corker proposes legislation to prevent Obama from unilaterally ending sanctions that Congress wrote into law. If all 54 Republicans and 13 Democrats agree on this point of constitutional integrity and institutional dignity, Obama’s promised veto of Corker’s legislation will be overridden.

Some who partake of Obama’s condescension say it is unseemly for the president to have to accommodate Chairman Corker, a former mayor (of Chattanooga). But one of the committee’s best chairmen since 1945 was a former mayor (of Indianapolis), Richard Lugar. And the chairman who in the 1940s tugged Republicans toward internationalism, Michigan’s Arthur Vandenberg, was a former publisher of a newspaper in Grand Rapids. For those who have forgotten the phenomenon, Corker’s patient bipartisanship is what a senator behaving senatorially looks like.

Iran surely construes Obama’s veto threat as evidence that, such is his hunger for an agreement, he will make concessions (about Iran’s nuclear infrastructure, the modalities of inspections and the removal of sanctions) that are unacceptable to Congress. The negotiations about such issues already have reflected asymmetries of desire.

Obama wants to prevent Iran from becoming a nuclear power, but more ardently wants, in the process of trying to do this, to encourage dynamics that will domesticate Iran’s regime and validate his claim to greatness. Iran desires relief from sanctions, but more ardently desires a nuclear capability.

Obama’s aspiration may be fanciful, but Iran’s regime is unlikely to be the first in world history to last forever. Iran’s aspiration may be sinister, but U.S. wars of regime change in Iraq and Libya have shown other nations the advantages of possessing nuclear weapons.

Obama’s obnoxious air of entitlement to unearned immunity from oversight should not blind us to this fact that has been obvious for some time: Iran is going to be a nuclear power if it intensely wants to be, and it does; no practicable sanctions can be severe and durable enough to defeat this determination.

The Middle East today is more resistant than ever to America’s healing touch. The 1990s disintegration of Yugoslavia demonstrated dangers that accompany nations — Serbia, Croatia, Bosnia, Kosovo — reasserting their sovereignties. Today’s Middle East convulsions demonstrate the greater dangers when nationality is eclipsed by sectarian tribalism. It is unclear what policy changes could give America much control over these events.

Arms control agreements that substantially alter nations’ arsenals become more possible as they become less important. That is, until events in other spheres make the adversarial nations less so. Having abandoned the unobtainable project of blocking Iran’s path to nuclear weapons, Obama has settled for trying to make the path longer and steeper. Even if the agreement merely extends the time during which Iran deceives inspectors to evade restrictions, time might matter.

Nothing is inevitable, but 10 years can be a long time in the life of a nation, especially when the regime is discordant with modernity: In 1979, the Soviets invaded Afghanistan; in 1989, the Berlin Wall came down.

With 80 million people (equal to Germany) and the world’s fourth-largest proven crude oil reserves, Iran is culturally ancient but demographically young. The median ages of Japan, the European Union, the United States and China are 45.5, 41.9, 37.3 and 35.1, respectively. Iran’s is 28. Fortunately, nations such as Egypt and Saudi Arabia are flexing their conventional military muscles, a necessary precursor to a balance of power. However precarious it might be, such a balance is a start to containing Iran.

Dealing with Iran is disagreeable, but not more so than depending on Stalin’s Soviet Union as a World War II ally more important than all other allies combined. Deterring a nuclear Iran might be even more problematic than was deterring the Soviet Union, depending on whether Iran’s theological intoxication is more than rhetorical. We are going to find out.

© 2015, Washington Post Writers Group