What many of them have argued for is a continuation of sanctions to deny the Iranians more resources to support their hegemonic ambitions and to try to compel them to accept a stronger agreement. Distorting your critics’ views to make them appear extreme is what you do when you operate a government like a campaign, not when you’re trying to build bipartisan support for something.

The president offered the most indefensible calumny in this debate in the very same statement in which he denounced Senator McCain. He likened domestic critics of the agreement to hardliners in Iran.

Those Iranian hardliners oppress an entire nation. They persecute women, gays, dissidents, and religious minorities. They murder children in the streets of Tehran. They provided weapons that were used to kill American soldiers in Iraq. They are terrorists, who killed innocent Jews in Argentina, and tried to kill the Saudi ambassador in Washington. They killed hundreds of Marines in Lebanon. They help Bashar al-Assad murder hundreds of thousands of Syrians. They control Hezbollah and Hamas. They are the implacable enemies of the U.S. and our allies and of every political ideal Americans have shed blood to defend.

Obama compared those murderous tyrants to Americans who worry the deal won’t prevent Iran from acquiring nuclear weapons. He compared them to freely elected American officials, some of whom, like John Kerry and John McCain, served our country in war, and don’t want to make it easier for Iran to commit more crimes against humanity and to dominate a greater expanse of the Middle East. That is a real example of partisanship that “crossed all boundaries.” And if Obama ever decides to be the kind of president he promised to be—a president who abhors tactics that aggravate the nation’s political divisions—he will apologize for it.