Joe Biden, speaking against a backdrop adorned with the trappings of a presidential address, including American flags and deep-blue drapery, delivered a scorching rebuke of Donald Trump’s stewardship of American foreign policy, accusing the president of bringing the country “dangerously close” to war with Iran.

Bernie Sanders quickly brought forward legislation to block funding for military force against Iran without congressional authorization, part of his argument that the “children of working families” disproportionately suffer the consequences of war compared with the “children of the billionaire class”.

Trump backs away from further military confrontation with Iran Read more

And Pete Buttigieg has increasingly emphasized his experience as a naval intelligence officer in Afghanistan to reassure voters that he has the experience to be president, arguing that someone who served in uniform would bring a nuanced and “forward-looking view” to future conflicts around the world.

Since Trump’s authorization of a drone strike killing the top Iranian commander Qassem Suleimani last week – and Iran’s launch of more than a dozen ballistic missiles at two US military bases in Iraq on Tuesday night – the top contenders for the Democratic nomination have treated the threat of further escalation as a clarifying moment in the final weeks before voting begins.

In a televised address on Wednesday, Trump backed away from the precipice of war with Iran, opting instead to impose new sanctions on Tehran in response to the retaliatory strikes. But his speech did little to soothe the growing political backlash in Washington, ensuring the issue was unlikely to go away any time soon

“At a time when Trump is pushing the nation closer to more reckless wars, I think people will start to look much closely at the records of the Democrats running to replace him to see which candidate they would feel safer with,” said Waleed Shahid of Justice Democrats, a progressive group.

He added: “Foreign policy does not always rank as a top priority for voters but it’s actually an area that falls much more under the president’s control than certain domestic policy issues.”

Facebook Twitter Pinterest Joe Biden makes a foreign policy statement on 7 January. Photograph: Justin Lane/EPA

Indeed, national security and foreign policy have so far played only a limited role in the Democratic primary, which has been dominated by healthcare, the economy and climate change. But the rising international tensions have reoriented the policy debate. Candidates are weaving foreign policy into their closing arguments to early-state voters, bringing into sharp relief long-simmering divisions within the party over matters of war and peace.

The initial response from the party’s presidential field was to condemn Trump for what candidates viewed as a reckless action that escalated tensions in the Middle East and could lead to an unintentional war with Iran. In the days that followed, however, the Democrats have amplified their disagreements, setting up what could be the first substantive debate among the candidates about the role of American power.

While it is too soon to gauge how Trump’s latest provocations toward Iran will resonate with voters, the occasion has provided both opportunities and risks for candidates.

Biden has billed his long record on foreign affairs and stature on the global stage as assets in a world rattled by Trump’s erratic foreign policy. On the campaign trail this week and during his formal speech in New York, Biden reminded voters of that résumé, which includes eight years traveling the world as Barack Obama’s lieutenant and two years serving as the chair of the Senate foreign relations committee.

“I understand better than anyone that the system will not hold unless we find ways to work together to advance our national interests,” Biden said in New York this week, waving off critics who say his commitment to bipartisanship is “naive or outdated”.

But while Biden presents his experience as an asset, his closest rivals have assailed that record, particularly his 2002 vote to authorize the war in Iraq and his role in shaping its aftermath. Sanders, who opposed the war in Iraq, recently suggested that the Biden’s foreign policy record could be a political liability against Trump should he be the nominee.

“Joe Biden voted and helped lead the effort for the war in Iraq – the most dangerous foreign policy blunder in the modern history of this country,” Sanders said on CNN. “I just don’t think that that kind of record is going to bring forth the energy we need to defeat Trump.”

Love is in the Brooklyn air as Elizabeth Warren gives campaign a shot in the arm Read more

Sanders meanwhile has seized on the rapidly unfolding conflict to emphasize his longstanding opposition to foreign wars as well as his efforts to end US military involvement in Yemen and prevent further action in Iran.

“I was right about Vietnam. I was right about Iraq. I will do everything in my power to prevent a war with Iran,” he tweeted. “I apologize to no one.”

While that message resonates with antiwar Democrats and independents, Sanders has yet to be seriously challenged on his views.

Elizabeth Warren shares Sanders’ anti-interventionist sentiments but finds herself on the defensive from critics on the left and the center as she attempts to reclaim her standing in the race. On Tuesday night she opened her rally in Brooklyn by addressing Iran’s retaliatory attacks.

“This is a reminder of why we need to de-escalate tension in the Middle East,” she said. “The American people do not want a war with Iran.”

Facebook Twitter Pinterest Elizabeth Warren at a rally in Brooklyn on Tuesday. Photograph: Joel Sheakoski/Barcroft Media

Buttigieg has used the occasion to highlight his military service and allay concerns about his youth and relative inexperience on the world stage. He has also assailed Biden supporting the “the worst foreign policy decision made by the United States in my lifetime”.

“This is an example of why years in Washington is not always the same thing as judgment,” Buttigieg said during an appearance on Iowa Press last month.

In the years since, Biden has called the 2002 vote a “mistake”, though recently he has been criticized for wrongly suggesting that he opposed the Iraq war from the outset in 2003. Even so, Democratic voters continue to say they trust Biden more than any other candidate on foreign policy.

In a CNN poll from November, 48% of Democratic and Democratic-leaning voters said Biden was best suited to handle matters of foreign policy. By comparison, Sanders ranked a distant second at 14%, while 11% said Warren and only 6% chose Buttigieg.

Whether the issue will continue to be a factor in the Democratic primary depends in part on what comes next. While polls tend to show that foreign policy is a low priority for voters, it has played a significant role in presidential elections since the September 11 terrorist attacks.

In 2004, growing opposition to the Iraq war helped to propel John Kerry to the presidential nomination. Four years later, Barack Obama wielded Hillary Clinton’s past support for the Iraq war as a cudgel, lifting him to the nomination. During the 2016 presidential election, Sanders and Trump tapped into a weariness over America’s “forever wars” and both attacked Clinton for her early support for the war.

Michael Carpenter, a former foreign policy adviser to Joe Biden and the senior director of the Penn Biden Center for Diplomacy and Global Engagement, said the recent tensions with Iran have afforded the former vice-president an opportunity to demonstrate his command of foreign affairs.

Facebook Twitter Pinterest New Yorkers protest against the Trump administration’s escalation of military tensions with Iran. Photograph: Justin Lane/EPA

“As voters contemplate how a confrontation with Iran could spiral out of control, they will contrast the erratic, unpredictable impulsive nature of the Trump presidency with the steady hand that Biden brings to the foreign policy arena,” he said.

But the congressman Ro Khanna, a national co-chair of Sanders’ campaign and a co-sponsor with the senator of the military funding legislation, said voters were tired after nearly two decades of war and hungry for a nominee who “offers a very different vision” of American foreign policy.

“He won’t win this debate in the Beltway but he’ll win it with American voters,” Khanna said.

Next week the candidates will meet in Des Moines for the final presidential debate before the Iowa caucuses on 3 February, and many party activists are eager for the Democratic frontrunners to clarify their views on how the US should engage in the world.

Alex McCoy, a Marine Corps veteran and the political director of Common Defense, a progressive veterans’ group, said the administration’s escalation toward Iran has given Democrats a crucial opening to reach out to voters who were drawn to Trump’s promise to end “forever wars” in 2016. And he believes it could make a difference in 2020.

McCoy pointed to research that showed the communities most devastated by casualties of America’s wars in Afghanistan and Iraq voted for Trump. The study found that “if three states key to Trump’s victory – Pennsylvania, Michigan, and Wisconsin – had suffered even a modestly lower casualty rate, all three could have flipped from red to blue and sent Hillary Clinton to the White House”.

“It’s common among pundits to say that voters don’t care about foreign policy. But that misses the truth,” he said. “Voters don’t care about the minutiae of treaty negotiations but they sure do care about whether the people they know and love are dying in forever wars.”