“The Iran deal is one of the worst and one-sided transactions the United States has ever entered into,” Trump said in a speech Friday.
The president said the Iranian regime has committed “multiple violations of the agreement,” and said his administration will be imposing additional sanctions on the country to block its financing of terrorism and its involvement in ballistic missiles.
WATCH: Trump threatens to terminate Iran nuclear deal if changes not made
But what exactly is the Iran nuclear deal and what does it mean if the U.S. is decertifying it?
What is the Iran nuclear deal?
In 2015, former president Barack Obama and the leaders of the United Kingdom, France, Russia, China, Germany and the European Union reached an agreement with Iran that required it to curb its nuclear program. In exchange, the deal lifted some sanctions on Tehran, that had previously hindered its economy.
At the time of the agreement, Obama said the deal would prevent Iran from obtaining a nuclear weapon.
WATCH: Obama praises Iran nuclear deal after sanctions were lifted
The agreement stipulates that Iran can possess only low-enriched uranium, which is not suitable for weapons, and it is limited to possessing no more than 660 pounds at any time.
Iran also agreed to provide the International Atomic Energy Agency (IAEA) greater access and information on the country’s nuclear program and to allow the agency to investigate suspicious sites.
The deal expires in 2025.
Has Iran complied with the agreement?
The IAEA has said Iran is complying with the deal. In July, Secretary of State Rex Tillerson also recertified Iran’s compliance with the deal.
However, on Friday Trump said Iran is not living up to the “spirit” of the nuclear deal.
Trump has previously complained Iran uses its new revenue to fund militant groups in the Middle East and develop ballistic missiles, which are not covered by the deal.
WATCH: Iran president says country will ‘honour’ nuclear deal if interests remain served
What is Trump’s role in the process?
The U.S. Congress requires the president to certify Iran’s compliance with the agreement every three months. Oct. 15 was the next deadline for certifying that Iran is complying with its terms.
Trump has previously called the landmark international deal an “embarrassment” and “the worst deal ever negotiated.” He said he believes the nuclear deal is too generous toward Iran and would not stop it from trying to develop a nuclear weapon.
In Friday’s speech, Trump reminded everyone that the deal “can be cancelled by me, the president, anytime.”
What does decertifying the Iran deal do?
While Trump did not pull the U.S. out of the agreement he gave the U.S. Congress 60 days to decide whether to reimpose the economic sanctions on Tehran that were lifted under the pact.
On Friday, Trump said the U.S is placing additional sanctions on Iran’s Revolutionary Guard for “supporting terrorism.”
This would allow Congress, which is controlled by the Republicans, to decide whether to kill the deal.
Iran has previously threatened it would restart its nuclear program if the U.S. reimposed sanction. Iran’s president said his country is capable of reviving its nuclear program within hours and quickly bringing it to an even more advanced level than when the deal was reached.
WATCH: Iran calls on Trump to stay committed to nuclear deal
Why are allies concerned?
Supporters say the deal’s collapse could prompt Iran to resume its nuclear weapons program, potentially triggering a regional arms race and worsening Middle East tensions. Opponents say it went too far in easing sanctions without requiring that Iran end its nuclear program permanently.
French President Emmanuel Macron said last week that there was no alternative to the nuclear accord.
The ambassadors to the United States from Britain, France, Germany and the European Union have all strongly backed the nuclear agreement as long as Tehran continues to comply with the pact.