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In May 2018, as president, he announced he would be formally pulling the U.S. out of the deal, which granted Iran sanctions relief and returning frozen assets to Iran in exchange for restrictions on its nuclear program and international inspections.
Since then, tensions between the countries have continued to escalate, leading to Iran shooting down a U.S. drone on Thursday.
Trump has said he does not seek war with Iran. But with conflicting signals coming from his advisers, military movements in the region and possible U.S. retaliation for the drone shootdown, a key question is whether rising tensions could turn into a military conflict, even an accidental one.
To review how we got to this point, here's a look back at the recent back-and-forth between the U.S. and Iran:
April 8, 2019: Trump administration designates Iran's Islamic Revolutionary Guard Corps a 'foreign terrorist organization'
President Donald Trump moved to designate Iran's Islamic Revolutionary Guard Corps, a wing of the Iranian military, as a foreign terrorist organization.
The designation was significant and controversial as it was the first time that the U.S. has officially identified a branch of a foreign state as a terrorist organization.
April 22, 2019: US ends waivers for Iran oil sanctions
The United States announced that it would no longer grant any waivers to countries to purchase Iranian oil, fully implementing the sanctions that President Trump reimposed in November as part of a "maximum pressure" campaign against Tehran.
May 5, 2019: Aircraft carrier sent to Middle East after indications Iran planned attack on US forces
The United States deployed an aircraft carrier strike group ahead of schedule, as well as a bomber task force to the Middle East in response to "clear indications" Iran and Iranian proxies were planning an attack on U.S. forces in the region, U.S. officials said.
A statement from National Security Adviser John Bolton said the deployments were intended "to send a clear and unmistakable message to the Iranian regime that any attack on United States interests or on those of our allies will be met with unrelenting force."
May 8, 2019: US imposes new sanctions on Iran's metal industries and Iran threatens to break the nuclear deal
The new executive order, signed by the president, authorized sanctions on Iranian iron, steel, aluminum, and copper sectors, which the White House said comprise 10 percent of Iran's export economy. The sanctions could also target financial institutions or foreign countries that facilitate Iran's export of those goods.
One that same day, Iran warned the nuclear deal's remaining signatories that it would stop implementing parts of the agreement if they don't improve economic cooperation with the country. In a televised address, Iranian President Hassan Rouhani said Wednesday that China, Russia, and those European powers have 60 days to improve economic ties with Iran or it will keep its excess enriched uranium and heavy water instead of shipping them overseas -- two requirements of the deal.
May 10, 2019: Pentagon deploys Patriot anti-missile battery to Middle East
The Pentagon announced that the U.S. military is deploying a Patriot anti-missile battery to the Middle East to further deter threats from Iran.
May 12, 2019: Iran or Iranian-backed proxies placed explosive charges the four ships
The initial assessment by a U.S. military team sent to assist the UAE is that Iran or Iranian-backed proxies placed explosive charges on the four vessels anchored off the coast of the United Arab Emirates, a U.S. official told ABC News. The official said each ship sustained a 5- to 10-foot hole at or below the water line.
May 24, 2019: More troops headed to the Middle East
An additional 1,500 U.S. troops and increased defensive capabilities are being sent to the Middle East to continue to help deter Iran, the Pentagon announced.
U.S. officials said the Iranian threat to U.S. forces continues even as Iran has pulled back some weapons systems. Two U.S. officials said that Iran has removed cruise missiles from two of the civilian shows that the Pentagon described as posing a risk to U.S. Navy ships, commercial ships and land targets.
June 2, 2019: Iran's Foreign Minister Javad Zarif says US sanctions are 'economic terrorism'
In an exclusive interview, Iranian Foreign Minister Javad Zarif told "This Week" Co-Anchor Martha Raddatz that "there will be consequences" if the United States keeps up its economic pressure campaign against Iran’s people.
Zarif labeled the new U.S. sanctions as "economic terrorism" that "targets ordinary Iranian people" because even though food and medicine are exempted from the sanctions, the financial transactions associated with them are not.
June 13, 2019: Two oil tankers attacked in the Gulf of Oman and Iran's Ayatollah Khamenei rejects Trump's offer to talk
Secretary of State Mike Pompeo blamed Iran for the attack on two commercial tankers sailing in international waters in the Gulf of Oman.
"The Department of Defense continues to closely monitor the activities of the Iranian regime, their military and proxies," the Pentagon said in a statement, adding, "The United States does not seek conflict with Iran, but we are postured and ready to defend U.S. forces and interests in the region."
On the same day, Iran's Supreme Leader said he has rejected an offer from President Donald Trump to talk, blasting the U.S. as insincere in its offer and untrustworthy.
"I do not consider Trump as a person worth exchanging any message with," Ayatollah Khamenei reportedly said.
June 17, 2019: Iran said that is was within 10 days of violating 2015 containment deal and then US announces deployment of additional troops to the Middle East
An Iranian atomic agency spokesman said that the country will break its uranium stockpile limit set by nuclear deal in 10 days.
Later in the day, the United States said it was sending 1,000 additional troops to the Middle East, amid rising tensions between the U.S. and Iran.
"In response to a request from the U.S. Central Command (CENTCOM) for additional forces, and with the advice of the Chairman of the Joint Chiefs of Staff and in consultation with the White House, I have authorized approximately 1,000 additional troops for defensive purposes to address air, naval, and ground-based threats in the Middle East," acting Defense Secretary Patrick Shanahan said in a statement.
June 20, 2019: Iran shoots down a U.S. drone
Iran, in what appeared to have been a major provocation, shot down what the U.S. military said was an unarmed and unmanned $130 million U.S. RQ-4A Global Hawk drone flying in international airspace over the Gulf of Oman near the Strait of Hormuz
Iran maintained that the American drone violated its airspace. Gen. Hossein Salami, commander of Iran's Islamic Revolutionary Guard Corps, offered a strongly worded threat to the U.S. after the drone was downed.
"Shooting down the American spy drone had a clear, decisive, firm and accurate message," he said, translated from Farsi. "The message is that the guardians of the borders of Islamic Iran will decisively respond to the violation of any stranger to this land. The only solution for the enemies is to respect the territorial integrity and national interests of Iran."
President Trump said that the Iranian shootdown of an American drone may have not been intentional, but a "mistake" by someone "loose and stupid."
He ordered a military strike on Iran late the same day, but reversed his decision after a plan was already underway, tweeting the next day he did so because he was concerned about the potential for casualties.