The US Congress could scuttle the nuclear deal with Iran this week. But it's unlikely to do so.

Donald Trump has railed against the deal since his campaign. In a speech on 13 October, Trump said 'the Iran Deal was one of the worst and most one-sided transactions the United States has ever entered into', reiterating the exact wording he had used the previous month at the UN General Assembly.

The US President must certify to Congress that Iran is in compliance with the deal's terms every 90 days, so Trump's October declaration that he 'cannot and will not make this certification' – despite multiple International Atomic Energy Agency assessments that Iran had adhered to the terms of the agreement – brought the US closer to withdrawal. Yet, rather than withdrawing, Trump passed the issue to Congress. The President's certification that Iran is in compliance with the deal is a requirement of the Iran Nuclear Agreement Review Act (INARA) of May 2015, bipartisan legislation co-sponsored by Senators Bob Corker and Ben Cardin, the top Republican and Democrat on the Senate Foreign Relations Committee.

Now, Congress has until 12 December to decide whether to reimpose sanctions on Iran that were lifted as part of the nuclear deal. Democrats are broadly supportive of the Obama-era agreement, and are therefore not willing to impose new sanctions that risk undoing the deal. When Democrats think about 'nuclear' and 'adversary' in the same sentence, they tend to consider North Korea rather than Iran. Why rip up the Iran nuclear agreement, ask many Democrats, when they would like to give a reason Kim Jong-un's regime to join the negotiating table? Within the Democratic Party, there is very little appetite for a pre-emptive military strike on Iran, which seems the only (albeit deeply flawed) alternate means to prevent Iran from acquiring a nuclear weapon.

Republicans would have to lead any push to impose new sanctions. Yet that, too, seems unlikely. Congress has known about the 12 December sanctions deadline since Trump failed to certify Iran's compliance with the agreement on 13 October. But there has not been the groundswell of comments by Republicans that would foreshadow new sanctions legislation.

Bob Corker, a retiring Tennessee senator, outspoken Trump critic, and chair of the Senate Foreign Relations Committee, holds the Senate post most empowered to push for new sanctions. But Corker recently warned that Trump was treating the presidency like 'a reality show', with reckless threats toward other countries that could set the nation 'on the path to World War III'. Nonetheless, Corker and his Arkansas colleague Tom Cotton, perhaps Trump's closest ally in the senate, started working on legislation in October to amend INARA. The effort to impose 'trigger points' on Iran's nuclear program would require 60 votes in the Senate, and hence the support of several Democratic Senators. The Corker-Cotton effort appears to have stalled.

Perhaps more importantly, outspoken Republican critics of the nuclear deal know that members of Trump's cabinet, including Secretary of State Rex Tillerson, have acknowledged that Iran is in compliance with the agreement. Furthermore, Secretary of Defense James Mattis, a leading Iran hawk from his time as commander of CENTCOM, recently told the Senate Armed Services Committee that the deal is in the US national security interest, and 'something that the president should consider staying with'.

Many Republicans privately resent Trump for passing responsibility on the issue to Congress. They have not coalesced around a viable alternative to the Iran deal, in part because it would be difficult to do so in light of Iran's compliance and support for the deal by respected figures such as Mattis. Republican opponents of the deal have had a difficult time explaining the benefits of US withdrawal. And many Republicans in Congress actually want to keep the deal intact: House Foreign Affairs Chairman Ed Royce called on Trump to 'enforce the hell out of' the agreement rather than withdrawing.

Finally, the sheer number of items on the agenda in Congress suggests there is little chance that new sanctions will be imposed. Republicans on Capitol Hill are working to reconcile the different House and Senate tax bills, hoping to iron out differences and then have Trump sign it into law, thereby notching the Republicans' first major legislative achievement this year. Meanwhile, there are ongoing negotiations about a potential government shutdown, a range of other legislation to be considered, ongoing sexual harassment charges against both Democrats and Republicans, and the distraction of the special Senate election on Tuesday in Alabama.

Trump might have passed the buck to Congress on the Iran deal. But, by all indications, Congress will pass the buck back to the President by refusing to either impose new sanctions on Iran, or amend the INARA legislation that requires the President to certify Iran's compliance with the deal. By January 2018 – the next deadline for Trump and the US in the Iran deal – it seems implausible that Trump will have been able to 'reach a solution working with Congress and [our] allies' that he desired in October. In such circumstances, Trump promised, 'the agreement will be terminated'.