President Donald Trump suggested this month that Lebanon is a “very small piece of the puzzle” he’s trying to put together in the Middle East. But Trump’s dismissiveness could cost him: Far from some ancillary fragment, Lebanon is the linchpin of the president’s dealings with Tehran.

Since retaking office, Trump has sought to undermine Iran by backing normalization between Israel and Lebanon while encouraging Beirut to take on its terror problem. That’s the right approach. Hezbollah, an Iran-backed Shiite militant group, erodes Lebanese sovereignty by using the country as a launching pad for attacks against Israel.

That makes it all the more bewildering that the Trump administration’s memorandum of understanding with the Iranians undercuts the president’s historic progress.

The very first point of the MOU, which declares a “permanent termination” of military operations in Lebanon, gives Iran a direct stake in Lebanon’s fate. “All this is a break that allows Hezbollah to go back and rebuild, rearm and re-strategize,” Hagar Hajjar Chemali, a former Lebanon and Syria director at the National Security Council, told me. Without enforceable details stipulating an end to Iran’s toxic involvement in Lebanon, the agreement just buys time for the regime to salvage its proxy.

“We’re not empowering the Lebanese,” Hussain Abdul-Hussain, a research fellow at the Foundation for the Defense of Democracies, told me. “We’re giving the keys of Lebanon to the Iranians.”

Even worse, the memorandum gives Tehran the resources it needs to help Hezbollah. If history is any lesson, the billions in unfrozen assets the regime is poised to reap from the agreement will not go to the suffering Iranian people; while protesters were being brutally persecuted throughout Iran last year, the mullahs sent $1 billion to Hezbollah. The war hasn’t convinced Iran to change its ways: Iran has reportedly promised Hezbollah financial support as soon as possible.

These concessions directly contradict the historic diplomacy that the administration continues to carry out between Lebanon and Israel.

Before the Iran war, Trump’s template for nudging progress in the Middle East was the Abraham Accords, the pact struck in his first term establishing diplomatic relations between Israel and the United Arab Emirates, Bahrain, Sudan and Morocco. That ambition extended to Lebanon, which hadn’t had direct diplomatic conversations with the Israelis for three decades.

This diplomatic track lives on, despite the president’s misguided MOU. Disarming Hezbollah, an imperative already enshrined in U.N. Security Council resolution 1701, has been a goal of ongoing diplomacy between the Israelis and Lebanese. During the fifth round of talks on Friday in Washington, the parties announced a new framework that includes Israel transferring two areas in southern Lebanon to the Lebanese military. The agreement is one of the most significant diplomatic breakthroughs between Lebanon and Israel in four decades, with both countries affirming a “shared goal of achieving lasting peace and security.”

For Israel, Hezbollah’s disarmament is nonnegotiable. The terror group has long attacked the country’s north, and Israel fears its tunnel network in the south could be used for cross-border operations.

For Lebanon, too, the stakes are existential. Lebanese President Joseph Aoun has framed Iranian interference as a direct threat to Lebanese sovereignty. “It’s not your country, it’s our country,” he said this month. Still, while Aoun is saying the right things, his government has avoided taking direct action against Hezbollah, hampered by political division and fears of sparking civil war.

And now, as the president seeks an end to the war in Iran, neutralizing Hezbollah is essential to the United States, too.

Ongoing U.S. negotiations with the Iranians focus heavily on nuclear weapons. But a nuke is a tool in service of a mission — the mission is spreading their radical Shiite revolution. As long as Hezbollah continues to operate in Lebanon, the revolution lives on — and so will the conflict.

Here’s the path forward: Trump is right that Israel can’t be the lone driver of Hezbollah’s disarmament. But the truth is that no outside power can do the job alone without risking a broader conflict that further cements Hezbollah’s place in Lebanon. His administration’s bet on empowering the Lebanese state is the right one. Now the president should double down.

At the same time, the Lebanese must do more to demonstrate that they are credible partners. That starts with taking small, tangible steps, like cutting off Hezbollah’s financial lines and purging its loyalists from the Lebanese Armed Forces. Israel’s agreement to transfer control of two “pilot zones” in Lebanon’s south to the LAF is the ultimate test: Can the force keep Hezbollah from operating? Is the Lebanese state ready to prove it can defend its own sovereignty?

Publicly committing to such bold moves is the best way Aoun can demonstrate to the White House his ability to help solve Trump’s regional headaches. Trump and Aoun are set to meet at the White House in mid-July.

The Iranians, of course, will continue to fight for control of Lebanon. In Switzerland this month, Iranian Foreign Minister Abbas Araghchi linked progress on Lebanon to ongoing negotiations with the United States. But “progress” to Iran means an opportunity to project its revolutionary dreams beyond its borders — the very thing the U.S. went to war to end. As long as Trump lets Hezbollah fester in Lebanon, he’s admitting defeat in Iran.