Iran is the biggest force of instability in the ever-dangerous, never-stable Middle East, so it’s not surprising that many political leaders and other observers obsess over Iran. Unfortunately, that obsession is misdirected when it focuses on the 2015 nuclear deal.

We think the deal was a mistake for several reasons — the acceptance of a nuclear Iran in a decade and the refusal to address Iran’s range of bad behaviors being the biggest issues. President Barack Obama negotiated from a position of weakness by making it clear that he wanted this deal as his signature foreign policy achievement, and he was wrong that the only options were the agreement his team negotiated and war.

But we can’t turn back the clock. U.S. foreign policy must work with the reality that a 2-year-old deal is in place, that neither our allies (Europe) nor our rivals (China and Russia) are going to reinstitute meaningful sanctions against Iran for anything short of a mushroom cloud, and that President Donald Trump’s propensity for throwing out his predecessors’ deals torpedoes hopes for negotiations from Pyongyang to Mexico City.

Rather than move toward breaking the deal, as Trump did by declaring it not in the nation’s best interest while questioning Iranian compliance, the United States needs to focus on handling Iran as the provisions of the Joint Comprehensive Plan of Action expire beginning in 2023.

A crucial part of that policy toward Iran must involve reversing the growth in its area of influence.

Iran doesn’t need nuclear weapons to undermine governments across the Middle East. It doesn’t need nuclear weapons to strengthen Hezbollah and other terrorist organizations. It doesn’t need nuclear weapons to kill Jews and pose an existential threat to Israel.

While Trump was correctly criticizing the nuclear deal and mistakenly pushing the Republican-led Congress to end U.S. participation in the accord, he was too busy celebrating what we hope will be the final days of the Islamic State caliphate in Iraq and Syria to focus on the future.

Iranian troops, in addition to Iranian missiles and other weapons, are based in Syria and, with the assent of Bashar Assad and Russia, appear determined to stay there. Iranian fighters also are in Iraq.

In effect, the world seems happy to trade a vicious terrorist organization operating as a nation (Islamic State) for a nation operating as a vicious terrorist organization (Iran).

We were encouraged by Secretary of State Rex Tillerson’s tougher talk about Iran’s non-nuclear military adventurism during his visit to Saudi Arabia on Sunday, Oct. 22. He urged Iranians and other foreign fighters who have battled Islamic State in Iraq to go home, and he warned businesses and nations not to work with the Iranian Revolutionary Guard Corps.

“Those who conduct business with the Iranian Revolutionary Guard, any of their entities — European companies or other companies around the globe — really do so at great risk,” he said.

That approach toward the conventional Iranian threat — lining up Arab allies and deterring European business opportunities — should take priority over fussing about the nuclear pact.