Both offered fierce critiques of Trump for pulling out of the Iran nuclear deal, which created the conditions for escalating tensions with the nation.

AD

But, while Biden withheld judgment on the wisdom of the drone strike itself that killed Iranian Maj. Gen. Qasem Soleimani, Sanders denounced the attack as “a dangerous escalation that brings us closer to another disastrous war in the Middle East.”

AD

Sanders compared the current moment to the months in 2002 before the Iraq invasion, when Congress voted on giving President George W. Bush permission to use military force in that country. Sanders opposed that measure, while Biden, then a senator from Delaware, supported it.

“I feared that it would result in greater destabilization in that country and in the entire region,” Sanders said during a town hall in Anamosa, Iowa, returning to a message he has used for months to highlight his difference with Biden. “At that time, I warned about the deadly so-called unintended consequences of unilateral invasion. Today, 17 years later, that fear has unfortunately turned out to be a truth.”

AD

Biden, also campaigning in Iowa ahead of that state’s Feb. 3 caucuses, sought to focus on Trump’s handling of his job.

AD

“The question is, does Donald Trump and his administration have a strategy for what comes next?” Biden asked at an event in Dubuque. “Unfortunately, nothing we have seen from this administration over the last three years suggests that they are prepared to deal with the very real risks we now confront.”

The sudden pivot in the policy focus of the presidential race — after a year focused on domestic issues such as health care, economic inequality and global warming — marked a return of a divide that has played a role in every Democratic nomination fight since the Sept. 11, 2001, terrorist attacks.

AD

Foreign policy and past support for the Iraq War were central to the debates that led to the nominations of John F. Kerry, who voted to authorize the Iraq invasion but often struggled to explain his views during his 2004 campaign, and Barack Obama, who in a heated 2008 primary had highlighted his opposition to the invasion as a contrast to rival Hillary Clinton’s vote as a senator to support it.

AD

Since then the disagreement inside the Democratic Party has shifted, as the nation has soured on decade-long foreign engagements on the other side of the world. Almost no one in the party continues to defend the vote to authorize the Iraq invasion, with Biden now saying he made a mistake in trusting Bush to use the power judiciously.

But a debate has emerged over whether the United States should more broadly pull back from its military involvement in the Middle East, echoing a similar shift in some corners of the Republican Party. Although Trump has promised to end what he calls “endless wars,” he has recently deployed more troops to the region than he has ordered home.

AD

On one side of the Democratic spectrum, Sanders and Sen. Elizabeth Warren (Mass.) have called for a rethinking of U.S. force projection overseas. In a series of tweets Friday, Warren described the drone attack as a part of Trump’s march toward war with Iran. After calling Soleimani “a murderer” on Thursday, she also joined Sanders in calling the drone strike an “assassination.”

AD

“The American people won’t stand for it,” she wrote of Trump’s Iran policy and the escalating tensions. “This is a moment for vigilance — for Americans to speak up and speak out.”

On the other side, candidates such as Biden, former South Bend, Ind., mayor Pete Buttigieg and Sen. Amy Klobuchar (Minn.) have called for a return to a more traditional form of Democratic foreign policy. Despite their criticisms of Trump, they have not offered views one way or the other on the prudence of the strike itself.

AD

The result is an emerging decision for Democratic voters.

“I think the basic choice is if you want a return to a recognizable, steady and robust American foreign policy or do you want a more wholesale rejection of the entire post 9/11 approach that Bernie and to some extent Warren are offering,” said Ben Rhodes, who worked as Obama’s deputy national security adviser and has not yet taken sides in the 2020 nomination fight. “The center of gravity has shifted.”

AD

Like Biden, Buttigieg and Klobuchar used appearances Friday to describe Soleimani as a dangerous American enemy and demand more information from the Trump administration about the strike and the subsequent plans to prevent a wider escalation of conflict.

AD

“I have a lot of questions and concerns about this, if you think about the repercussions of what this is going to mean,” Klobuchar said at a campaign stop in Waterloo, Iowa. “I’m going to demand a briefing on this from the White House.”

Buttigieg, who decided to break recent precedent and keep on his suit jacket to speak with voters Friday, echoed those same comments.

“America is going to be asking those questions in very serious terms over the next few days,” Buttigieg said at a stop in Conway, N.H. “As a military intelligence officer on the ground in Afghanistan, I was trained to ask these questions before a decision was made.”

AD

He did not repeat criticism he had leveled against Biden earlier in the week. When asked about his foreign policy experience relative to fellow candidates at events before the strike, Buttigieg repeatedly told reporters that Biden’s vote in favor of the Iraq War — “the worst foreign policy decision of my lifetime” — demonstrates that “tenure is not the same as judgment.” Buttigieg, 37, was an undergraduate student at Harvard University when the vote was taken in October 2002.

AD

Sanders also has stepped up his attacks on Biden in recent days, telling The Washington Post this week that the former vice president brings “a lot of baggage” to the campaign, including his 2002 support for authorizing force in Iraq. Asked Friday in Cedar Rapids about that attack, Biden said he would not respond to Sanders’s “ridiculous” comments.

“You’re not going to get me in a fight with Bernie,” Biden said. “Bernie’s got enough baggage.”

AD

Until Friday, foreign policy had largely been a sideshow in a Democratic contest dominated by finding a way to defeat Trump. When it arose in debates, or on the trail, the candidates have mostly stuck with broad critiques of Trump’s geopolitical outlook, his decision-making process, or his treatment of U.S. allies and apparent affinity for authoritarian figures.

AD

All of the top-polling candidates have denounced Trump’s decision to leave the Iran nuclear agreement struck by Obama, and all support rejoining the deal if Iran returns to compliance.

Each of the senators still in the race, Warren, Klobuchar, Sanders, Cory Booker (N.J.) and Michael F. Bennet (Colo.), have co-sponsored a bill that would require Trump to seek congressional authorization to launch “kinetic military operations in or against Iran” absent a national emergency created by an attack on U.S. interests.

AD

The candidates also have made clear that they are impatient with continued military deployments that began after the 2001 terrorist attacks. Buttigieg has promised a withdrawal of most military forces in Afghanistan by the end of his first year in office, while Biden, Klobuchar, Sanders and Warren have promised to accomplish that goal by the end of their first term.

To the extent foreign policy has been an issue previously, Biden has largely been the beneficiary, since his campaign is anchored in selling his decades of international experience. Although he supported the Iraq War authorization, he repeatedly argued for more dovish positions in the Obama administration, pushing against the Afghanistan surge of troops in 2009, opposing the 2011 U.S. military intervention in Libya and expressing caution about the plan to kill Osama bin Laden.

In an October CNN poll, 56 percent of Democratic-leaning voters said Biden would best handle issues of foreign policy, well ahead of the 13 percent who named Sanders and the 11 percent who named Warren. But other polls have shown that foreign policy trails a number of other issues, including health care, the environment, taxes and the economy, in the order of importance for those same voters.

At the events in Iowa, Biden’s foreign policy qualifications are a frequent point of praise from his supporters. Tom Avenarius, 69, of Dubuque, who served as an Army combat engineer in Vietnam from 1970 to 1971, said Friday that international experience was one of the reasons he leans toward Biden.

“Joe knows a lot of foreign ministers and presidents, so I think he’d be able to talk with people,” he said.

But to Sanders supporters, foreign policy is often just as important a draw to the Vermont firebrand. Randy Harrington, a self-described “Bernie Bro” from Iowa City who wore a “Feel the Bern” hat to a Sanders town hall at the National Motorcycle Museum on Friday, said he worried that the killing of Soleimani could lead to a volatile situation in the Middle East.

“Endless wars, it just, it sucks,” said Harrington, 67, his voice dripping with disgust. Harrington said he grew up protesting the Vietnam War and has grown tired of seeing decades of conflict.

“It’s very scary,” he said. “And I think us being over there — it makes it worse.”

Chelsea Janes in Conway, N.H., Cleve Wootson and Holly Bailey in Dubuque, Iowa, David Weigel in Waterloo, Iowa, and Sean Sullivan in Anamosa, Iowa, contributed to this report.