It was the third meeting between Donald Trump and Kim Jong Un in just over a year. The first Trump-Kim summit took place in Singapore in June last year. A meeting in Hanoi, Vietnam, was held in February 2019. Both meetings failed to provide a clear roadmap for North Korea's denuclearization.

Trump made history on June 30 with his latest encounter with Kim. He's the first sitting US president to visit the Demilitarized Zone (DMZ) that divides South and North Korea. Trump briefly crossed into North Korea as he shook hands with Kim. He said he was "proud to step over the line."

Prior to his meeting with Kim, Trump flew to the DMZ with South Korean President Moon Jae-in. The US president met with South Korean and American troops as he watched over North Korea from a military post in the DMZ. US presidents in the past have visited American troops on the South Korean side but not set foot in the DMZ.

From calling Kim Jong Un "little rocket man" to someone he has a "certain chemistry" with, Trump has come a long way in his dealing with North Korea. On June 30, he once again emphasized his personal ties with the North Korean dictator. Kim, too, hailed his "wonderful" relationship with Trump, saying the latest meeting would enable nuclear talks.

Washington and Pyongyang blame each other for the impasse over nuclear talks, but Trump is hopeful for a breakthrough. Although his previous two meetings with the North Korean leader didn't yield any result, Trump said he was "in no rush" to defuse tensions on the Korean Peninsula.

Experts have warned that North Korea may never agree to fully give up its nuclear ambitions, which they say Pyongyang views as vital for regime survival. In March, new satellite imagery suggested that North Korea started rebuilding a rocket launch site before Kim and Trump's Vietnam summit in Feruary. The site had been dismantled last year as part of Kim's denuclearization pledge.

Director of National Intelligence Dan Coats resigned from his post, which oversees and coordinates all 17 US intelligence agencies, in July 2019. Coats clashed with Trump on Russia, taking a harder line on Vladimir Putin than the president. He also contradicted Trump's assertion that North Korea no longer posed a threat.

Labor Secretary Alexander Acosta announced his resignation in July 2019, after criticism of a legal deal made years ago that led to financier Jeffrey Epstein only serving 13 months in jail for child sex abuse.

Deputy Attorney General Rod Rosenstein submitted his resignation at the end of April 2019, after a two-year run defined by his appointment of a special counsel, Robert Mueller, to investigate connections between Donald Trump's 2016 campaign and Russia. The move made Rosenstein a frequent target for Republican wrath and angry Trump tweets. Indeed, he often appeared to be on the edge of being fired.

Randolph Alles, a former Marine who reached the rank of major general, resigned as the head of the US Secret Service in early April 2019. Although initial news reports suggested he had been "fired," he later said he had been notified of changes to senior security positions and that he resigned voluntarily. He had previously served as acting deputy commission of US Customs and Border Protection.

Kirstjen Nielsen announced her resignation as secretary of homeland security in early April 2019. She had previously served in other administration positions, including deputy White House chief of staff. Nielsen, a hard-line border security advocate, is best known for her controversial policy of separating children from their migrant parents at the US border.

Bill Shine announced his resignation as White House communications director in early March 2019. The former Fox News executive may be leaving his post, but he's not completely out of a job. The White House has said he will be working on Trump's 2020 reelection campaign.

Brock Long announced his resignation as the head of the Federal Emergency Management Agency (FEMA) mid-February 2109. Long is best known for managing the agency's response to historic wildfires in California and major landfalls of powerful hurricanes. However, his resignation came shortly after he was told to reimburse the government over the misuse of government vehicles.

Appointed by Trump's predecessor Barack Obama in 2015, McGurk was the US envoy to the coalition fighting "Islamic State" terrorists and was influential in shaping US policy in northern Syria. He was due to end his tenure in February 2019 but stepped down days after Defense Secretary Jim Mattis, largely due to Trump's sudden decision to take US soldiers out of Syria.

Defense Secretary Jim Mattis abruptly announced his retirement in late December 2018 after Trump ignored his advice and announced the complete withdrawal of US troops from Syria. Mattis' resignation letter laid bare the growing divide between them, criticizing his boss for his treatment of allies. Mattis was a keen supporter of NATO and traditional US alliances, putting him at odds with Trump.

Interior Secretary Ryan Zinke resigned in December 2018 as pressure mounted from more than a dozen investigations into various aspects of his tenure and private business. The former Navy SEAL was a leading advocate of expanding domestic energy production, opening up vast swathes of the country for exploration.

In December 2018, Trump announced that John Kelly, his third chief of staff, would step down at the end of the year. He had been brought in to establish order in the Trump White House but found the job arduous, and his relationship with his boss soured. The retired four-star Marine Corps general was replaced by budget director Mick Mulvaney, after several candidates turned down the job.

Attorney General Jeff Sessions was fired in November 2018 after several months of abuse from Trump. Despite being an early supporter, he attracted the wrath of his boss early on by recusing himself from the Justice Department investigation into collusion. He was replaced with a loyalist who shares Trump's concerns about the investigation.

United Nations Ambassador Nikki Haley, one of the administration's few high-profile women, announced her resignation in October 2018. She said her resignation was long-planned, but the announcement took most senior politicians by surprise. She lent international legitimacy to the administration as she attempted to provide a coherent message.

The White House director of legislative affairs announced he would leave his post effective July 20, 2018. Short, one of the administration's longest-serving members, was also one of its most visible, pushing Trump's legislative agenda on TV. But his work was frequently undercut by the president, who complained about deals the team had negotiated, preferring instead to go it alone without them.

It remained a mystery to many how Pruitt could hang on for so long, but the president seemed to like him. Many on the left cringed at his every move as head of the Environmental Protection Agency. He was also embroiled in various ethics scandals. Nevertheless, Trump took to Twitter to thank Pruitt for doing an "outstanding job" at the EPA.

One of Trump's top lawyers in the ongoing special counsel investigation into Russian involvement in the 2016 presidential election, Cobb said he simply wanted to retire. But many believe he was forced out by Trump and others in his legal team for his lack of aggression in Robert Mueller's Russia probe. Cobb was said to have been increasingly uneasy about Trump's Twitter attacks on Mueller.

White House Homeland Security Adviser Tom Bossert, who had worked for George W. Bush, was reportedly pushed out in the shake-up that occurred after John Bolton replaced H.R. McMaster as national security adviser. It is said that Bolton had no issues with Bossert, but that he wanted his own team in place. The White House thanked Bossert for his "patriotic service" and wished him well.

Though the White House said Shulkin resigned, he says he was fired. A holdover from the Obama administration, he was appointed to run the Department of Veteran's Affairs by Trump. His downfall came amid a travel expense scandal involving his wife. He criticized the atmosphere in the administration as "toxic, chaotic, disrespectful and subversive," claiming he was the victim of political intrigue.

In a tweet on March 22, 2018, US President Trump announced he was replacing H.R. McMaster with John Bolton as his national security adviser. A respected general, McMaster said he would retire from the US army and public service. McMaster's departure was not a complete surprise, as he and Trump are reported to have had conflicting views on a number of US policies.

A former Exxon executive, Tillerson had served as secretary of state for a little over a year. Donald Trump ousted Tillerson in order to form a "new team" ahead of talks with North Korea, adding that he and Tillerson "disagreed on things." The relationship between them is said to have deteriorated after Tillerson reportedly called Trump a "moron" in October 2017.

A Goldman Sachs veteran, Gary Cohn served as Donald Trump's top economic adviser at the head of the National Economic Council. He helped push through controversial tax reforms in 2017. However, Cohn stepped down in March 2018 after failing to persuade Trump to give up his idea of imposing tariffs on imported steel and aluminum.

Hope Hicks resigned from her post as the White House communications director in late February 2018. A day before resigning, she testified before US lawmakers on Russian interference. She admitted to telling "white lies" for Donald Trump, but not related to Russia. The White House insisted her resignation was not linked to the testimony. The 29-year-old was among Trump's closest aides.

The White House staff secretary handed in his resignation after his ex-wives accused him of domestic abuse. Despite resigning, Rob Porter denied the allegations as "simply false." Trump initially defended Porter, and the US media questioned how Porter passed his background check for the job. Recently, reports surfaced of a romance between Porter and Trump's longtime aide Hope Hicks.

He played a key role in getting Donald Trump into the White House, but even chief strategist Stephen Bannon was ousted within a year. Bannon was a champion of economic nationalism and Trump's "America First" strategy. After the fallout of white supremacist violence in Charlottesville mid-August, Bannon agreed to leave the administration.

The 53-year-old former hedge fund investor nicknamed the "Mooch" was communications director for just 10 days. The colorful New Yorker filled a dream role that had been vacant for months, but was forced out on the same day that straight-shooting former Marine Corps general John Kelly became chief of staff. Trump was displeased with his infamous expletive-laden rant against other senior staff.

Walter Shaub, the former director of the Office of Government Ethics, resigned in July 2017 after clashing with the White House over Trump's complicated financial holdings. Shaub reportedly called Trump's administration a "laughingstock."

Reince Priebus, former White House chief of staff, was forced out just six months into his tenure after a public feud with Anthony Scaramucci, the White House communications director. Priebus was reportedly among those West Wing staffers who had opposed hiring Scaramucci.

Sean Spicer, who had a fraught relationship with the president and the press, resigned after telling Trump he vehemently disagreed with the selection of Anthony Scaramucci as White House communications director.

Michael Dubke, former White House communications director, was asked to leave in May 2017 over what was perceived as his poor handling of allegations of Russian involvement in the US election.

US President Donald Trump fired FBI Director James Comey — allegedly over how he handled the Clinton emails investigation. Critics, however, believe the FBI's probe into Trump's campaign ties with Russia was the real reason.

Trump's national security adviser, Michael Flynn, resigned in February 2017 after revelations that he had discussed US sanctions on Russia with the Russian ambassador to the US before Trump took office, and then misled Vice President Mike Pence about the conversations.

US President Donald Trump fired his National Security Adviser John Bolton saying he disagreed "strongly" with his suggestions. Trump had tweeted that Bolton's "services are no longer needed at the White House."