Donald Trump’s declaration earlier this month that he intends to withdraw from the Iran nuclear accord—the “worst deal ever,” as he loves to say—unless lawmakers on Capitol Hill made it broader and tougher, was “the equivalent of pulling the pin out of the grenade and handing it to Congress,” one Democratic congressional aide told me. Now Congress has 90 days—when the president has to recertify the deal—to put the pin back in. But, as in an action movie, it’s a task that currently looks impossible. The legislation that the Senate devises will have to garner 60 votes and also satisfy the Trump administration, which wants lawmakers to strengthen restrictions on the regime’s behavior. If Congress fails to deliver, Trump will unravel his predecessor’s signature foreign policy achievement. Meanwhile, the Iranians have said that any move by the Trump administration to unilaterally change the terms of the agreement would be viewed as a breach, potentially starting their race for a bomb.

Without one party or another adjusting their stance, it gets down to the same game of chicken: who’s going to blink? The Trump administration theory seems to be that if everything blows up, Congress—maybe even the Democrats in Congress—get the blame for being soft on Iran. “The rhetoric is intellectually dishonest,” says a highly placed source at the State Department. “I understand the political, domestic lens with which people look at this, but the facts are that it doesn’t need to be a Congressional issue . . . [The White House is] just punting it because there were no good options for what they wanted to do . . . This way, they could just say, ‘we’re doing it,’ and have a scapegoat lined up.”

It seems a long shot that Trump’s buck-passing gambit can succeed, even on the highly limited terms of casting the blame of a catastrophic Iran failure on others. But meanwhile, Capitol Hill is left with a slate of terrible options. After all, no one wants to cast a vote that appears to be in favor of Iran, given its hegemonic aspirations in the Middle East, not to mention its implacable hostility to Israel. “Look, there are going to be no defenders of the Iran deal domestically. It is very unpopular in that Iran still evokes this ‘Axis of Evil’ [narrative] among people,” the State Department staffer said. “When you look at it through that lens—even though I think strategically it makes Americans safer—that is a tough sell.”

The alternative may open the door to a nuclear Iran and global opprobrium. “If we unilaterally renegotiate the agreement, we will be in violation of it—not Iran. And ultimately, we will be isolated because of it—not Iran,” a former State Department and National Security official told me.

And if Congress does nothing, Trump says he will pull out anyway. “Maybe it’s a bluff,” the second Capitol Hill aide suggested to me after Trump’s announcement. “But it’s a bluff with unthinkable consequences.”

With a majority of 52 to 48 in the Senate, Republicans can’t avoid leading the effort. And to further complicate matters, Congress can snap back the previous nuclear sanctions against Iran with a simple majority vote within a 60-day window that began with Trump’s announcement, under a bill known as the Corker-Cardin law, which was passed in 2015. “The ball is really in their court now,” the first congressional staffer said of Mitch McConnell and Paul Ryan. “[Chuck] Schumer and [Nancy] Pelosi are not going to jump in front of this thing. They’re going to let Republicans lead, and see what they come up with, and we’ll have to decide whether we can go along with it or not.” But there is a concern that after suffering a string of legislative failures, the G.O.P. might turn Trump’s jump ball into a partisan win. The second Congressional staffer said, “The minute this turns into something with a lot of real political pressure, it just becomes dangerous.”