Candidate Donald Trump denounced the 2015 nuclear deal with Iran as "catastrophic" and "the worst deal ever." He's been itching to withdraw the United States from the deal ever since.

So it's no surprise that, by a Sunday deadline, Trump will almost certainly refuse to certify to Congress that the deal serves the national security interest of the United States. This gesture won't immediately unravel the deal. Instead, it will kick the can to Congress, which must decide within 60 days whether to restore nuclear-related sanctions. That would violate the agreement.

Yet the Trump team apparently believes the implied threat will bludgeon Tehran into accepting harsher terms — and behaving better in the Mideast. In reality, Trump's obsession with undoing the Iran deal is more likely to worsen the growing military threat Iran poses to Israel and America's Arab allies.

How so?

The agreement (known as the Joint Comprehensive Plan of Action, or JCPOA) addresses only one element of the threats posed by Iran – its nuclear program. The deal wasn't meant to curb Tehran's growing missile program and its ever-growing support for Hezbollah and Hamas. Nor did it touch on Iran's massive penetration of Syria up to Israel's border via Shiite militia proxies led by Iranian Revolutionary Guard cadres. This deal was only about nuclear weapons.

These other threats must be addressed and soon. But if the JCPOA should collapse as a result of the reimposition of U.S. sanctions, Tehran will be free to restart its nuclear program. Can you imagine the difficulty of curbing Iranian expansionism if the ayatollahs have nukes?

That's no doubt why Secretary of Defense James Mattis affirmed, in congressional testimony this month, that it was in our national security interest at the present time to remain in the deal.

It's also why former Israeli national security adviser Uzi Arad made the rounds in Washington, urging members of Congress and the administration to preserve and strengthen the agreement. "Doing away with the agreement is no real option," said Arad, who advised Israeli Prime Minister Benjamin Netanyahu, a harsh opponent of the Iran deal. Like many in Israel's national security establishment, Arad believes that dumping the deal "removes … assets and certain things that are tangible … replacing that [with] nothing."

In other words, a move that ends the deal could prove disastrous for curbing Tehran.

Of course,  punting the problem to Congress doesn't automatically derail the agreement, and many legislators on both sides of the aisle recognize the danger in undoing it.

But strong opponents, like Sen. Tom Cotton (R., Ark.), who has the president's ear, want Congress to demand that Iran accept new terms for a deal or else face renewal of nuclear-related sanctions. "Congress and the president, working together, should lay out how the deal must change  and, if it doesn't, the consequences Iran will face," Cotton told the Council on Foreign Relations. "When Iran has made it clear that they don't take seriously our interests, then at that point it may be time to reimpose sanctions."

That kind of threat will be rejected by Tehran.

Moreover, the other parties to the deal — France, the United Kingdom, Germany, Russia, and China — will blame the U.S. for abrogating the agreement. Especially since, as attested to by international inspectors, Iran has made no material breach of its terms.

None of the above means that Washington should not act to curb Iranian missiles and misbehavior — or negotiate a follow-on deal that would extend its time frame. New nonnuclear U.S. sanctions against Hezbollah and Iran's Revolutionary Guards would be well advised.

Moreover, European allies, led by France, are eager to work with the U.S. to give teeth to U.N. sanctions against Iran's missile program — and to work on extending the life of the Iran deal and demanding inspection of suspect Iranian military sites.

But undercutting the agreement would only undercut a strong allied response.

Ironically, the Trump administration is supposed to unveil a broader strategy to curb Iranian military aggression in the Mideast by Oct. 30. This is the moment when the administration should be working across the aisle, and with allies, on a broad approach to dealing with Iran.

"Now should be the time for both sides of the Washington debate on Iran to come out of their foxholes," writes the Brookings Institution's Suzanne Maloney, "and find common ground … including efforts to address the unavoidable compromises in the JCPOA, such as seeking to extend its sunset provisions. Instead the Trump administration is on the verge of upending the hard-fought checks on Tehran's nuclear ambitions."

There's an odd twist to Trump's approach. President Barack Obama, in his eagerness for an Iran deal, was willing to put aside efforts to curb Iran's Mideast aggression, which left Tehran free to expand its grip on parts of the region. Now Trump, in his eagerness to get rid of the Iran deal, may make it harder to stop Iranian expansion in the near future.

Decertifying the Iran deal opens a Pandora's box with no one certain what will emerge.