Former Vice President Joe Biden and Vermont Senator Bernie Sanders emerged as the only candidates with the chance of winning a majority of delegates following a lengthy primary season as the undisputed frontrunners in the race for the Democratic Party ticket.
Barring unforeseen events at a contested convention in July, it is all but certain one of the two men, who are both in their late 70s and have long track records as elected officials, will face US President Donald Trump in the general election in November.
If either Biden or Sanders win in the general election, they will have a major hand in forming US foreign policy in the wake of an administration whose so-called "America first" approach to diplomacy has reshaped the role of the US in the world and altered how Washington is viewed by allies and foes alike.
So far in the race, foreign policy has been far from central topic, with Senior Vice President of the Council on Foreign Relations James M Lindsay noting that talk of US strategy abroad was "AWOL" in the Democratic debate in Las Vegas on February 19, adding that the omission "could be a metaphor for foreign policy's role in the 2020 campaign".
While relegated to the margins, foreign policy has not been completely absent from the race, with both Sanders and Biden pledging to undo hallmark Trump foreign policy measures. Both have derided Trump's Middle East plan, which the administration has touted as a road map to peace between Israel and Palestine.
The candidates have also used the foreign policy as a wedge in recent weeks, with Sanders, an avowed anti-interventionist, seizing on then-Senator Biden's 2002 vote in favour of the US invasion of Iraq. Biden has repeatedly called the vote a mistake.
During a February debate in South Carolina, Biden had accused Sanders of not condemning the authoritarian governments of Cuba and Nicaragua, referring to Sanders's previous praise for Havana's education policy. Sanders called the claim "categorically untrue".
Here is where both the key candidates stand on foreign policy:
Biden, 77, served for almost 40 years as a senator from his home state of Delaware, and then for two four-year terms as vice president in the administration of former President Barack Obama, and often references his foreign policy qualifications when pitching himself as the candidate to beat Trump.
The former vice president, who served as the highest-ranking Democrat on the Senate Foreign Relations Committee for 12 years, has promised a complete reversal of Trump's policies if elected president, framing his foreign priorities around combatting the "strongmen and thugs" of rising authoritarianism across the globe, restoring alliances, and re-establishing the US leadership, in particular in fighting climate change and promoting democracy.
"If we give Donald Trump four more years, we'll have a great deal of difficulty of ever being able to recover America's standing in the world and our capacity to bring nations together," he said. "I think it'd be catastrophic to our national security and to our future. We can't let it happen."
The travel ban imposed by the Trump administration on several majority Muslim countries would be removed under Biden and he would end the US support of the Saudi war in Yemen, he has said.
Biden has promised that the continuing conflicts in the Middle East and Afghanistan, where a recent deal struck between the Trump administration and the Taliban aims for an eventual withdrawal of all US troops, would also be reassessed.
He has also stressed a need for steady leadership in the Middle East, as opposed to a complete overhaul of the US strategy, with an approach to "counterterrorism" that utilises special forces teams and airstrikes to combat specific groups, as opposed to large troop deployments.
During the third Democratic debate in 2019, Biden again said his 2002 vote in favour of the US invasion of Iraq was a mistake, saying he "never should have voted to give Bush the authority to go in and do what he said he was going to do".
Biden has also long called for a two-state solution in the Israel-Palestine conflict, and has criticised the Trump's Middle East Plan. "A peace plan requires two sides to come together. This is a political stunt that could spark unilateral moves to annex territory and set back peace even more," he said of the plan.
Palestinian officials should do more to condemn violence against Israel, Biden has said, while Israeli officials should stop the expansion of settlements. He told the New York Times he does not think the US embassy in Jerusalem should be moved back to Tel Aviv.
Sanders, 78, the longest-serving independent in the history of Congress, has framed his foreign policy through the belief that it is inextricably linked to domestic policy, and has full-throatedly criticised the history of US military intervention abroad.
In an op-ed in June 2019, Sanders said he would rethink the US foreign policy, extricating the country from wars in the Middle East and reorienting strategy to prioritise "diplomacy and working collectively with allies" over military action.
He has argued that his vision does not involve a US retreat from the world stage, but rather the use of diplomacy and cooperation instead of force to further US interests.
"We need to rethink the militaristic approach that has undermined the United States' moral authority, caused allies to question our ability to lead, drained our tax coffers, and corroded our own democracy," he wrote.
He has also said he would completely withdraw US troops from Afghanistan, while blasting the so-called "war on terror" as "staggeringly wasteful" and leading to the proliferation of terrorism, not its destruction.
"American power should be measured not by our ability to blow things up, but by our ability to build on our common humanity, harnessing our technology and enormous wealth to create a better life for all people," Sanders wrote.
Sanders has said he will overturn Trump's travel ban while putting a moratorium on deportations pending an audit of policies and practices. He has also said he would end the US support for Saudi forces in Yemen.
When it comes to Israel-Palestine, Sanders has been outspoken. He has said he supports a two-state solution to the decades-old conflict while opposing the US decision to move its embassy to Jerusalem from Tel Aviv.
He also criticised statements by Secretary of State Mike Pompeo that backed Israel's right to build settlements in the occupied West Bank - which the US had long maintained were an obstacle to peace between Israelis and Palestinians.
"Israeli settlements in occupied territory are illegal. This is clear from international law and multiple United Nations resolutions," Sanders tweeted after Pompeo's announcement.
In regards to Trump's Middle East plan, Sanders has said it "doesn't come close" to being in compliance with international law and would only perpetuate the conflict.