Leading candidates in the Democratic primary were united in describing Gen. Qassem Soleimani as a murderer responsible for the deaths of Americans. But they also slammed Trump as reckless and ill-prepared for the consequences — and retaliation — likely to follow the killing.

Former Vice President Joe Biden charged Thursday that Trump "tossed a stick of dynamite into a tinderbox." Massachusetts Sen. Elizabeth Warren said the the move "'increased the likelihood of more deaths and new Middle East conflict."

Vermont Sen. Bernie Sanders slammed what he called a "dangerous escalation" that puts the United States "on the path to another war — potentially one that could be even worse than before."

The foreign policy focus, at least for a day, marked a sharp shift for a Democratic primary that has so far been dominated by domestic policy concerns such as health care, the economy and immigration. The narrow focus reflects the relative inexperience of the large Democratic field on the international stage as well as voters' priorities after nearly two decades at war.

But the rising tension with Iran is shifting the debate just a month before voting begins in Iowa. That new debate is likely to revive fights between centrist Democrats and Democrats on the left who are skeptical of military intervention.

Biden, who has more foreign policy experience than the rest of the field combined, could benefit from the sudden attention to global affairs, though his long record in complicated foreign entanglements creates vulnerabilities that critics in both parties are trying to exploit.

That intraparty fight starring Biden had begun even before Trump authorized the strike that killed Soleimani.

Earlier in the week, Pete Buttigieg — the now-former mayor of South Bend, Indiana — criticized Biden for voting to authorize the Iraq War, calling it part of the nation's "worst foreign policy decision" of the 37-year-old's lifetime. On Friday, Buttigieg, a former military intelligence officer, didn't call out Biden by name but made reference to the Iraq War while addressing the airstrike: "This must not be the beginning of another endless war."

Sanders initially described Trump's decision as an "assassination." Facing voters in Iowa on Friday, he also noted his opposition to the Iraq War and reiterated his warnings from over a decade ago that U.S. intervention there would destabilize the region. He said the outcome in Iraq should act as a guide for foreign policy now.

"We face a similar crossroads fraught with danger," Sanders said, insisting that the U.S. must commit to ending its military presence in the Middle East.

Hawaii congresswoman Tulsi Gabbard, a combat veteran who has long criticized U.S. policy in the Middle East, called the killing of Soleimani "an act of war" committed without authorization from Congress.

Colorado Sen. Michael Bennet, a moderate who has struggled to get traction in the 2020 contest, was critical of Trump's move during an interview but also said, "Democratic voters should think critically about politicians who voted for the Iraq War."

"That was a terrible vote," he added, referring to Biden's support for the war.

Biden, meanwhile, has not aggressively defended his vote. On Friday, he focused on Trump, raising doubts about the president's ability to handle the complex geopolitics involved.

"The risk of nuclear proliferation is real. And the possibility that ISIS will regenerate in the region has increased," Biden said, using a common abbreviation for the Islamic State group. "And the prospects of direct conflicts with Iran is greater than it's ever been. The question is, Do Donald Trump and his administration have a strategy for what comes next?"

Biden aides privately acknowledged, with some frustration, that foreign policy hadn't been a focus of the Democratic nominating fight.

A top Biden adviser, who spoke on condition of anonymity to discuss the campaign's thinking, said the campaign is not concerned about some Democrats, including Sanders, reminding voters that Biden supported the use of military force of Iraq. The adviser said the Biden team believes most voters will weigh Biden's total record positively against Trump's "erratic" approach, rather than focus on one Senate vote.

Biden used the conflict in a fundraising message Friday, asking donors to chip in at least $5 after warning that the U.S. "could now be on the brink of a major conflict across the Middle East."

"It's more clear than ever that we need strong, steady, experienced leadership," he wrote.

Trump said he ordered the airstrike because Soleimani had killed and wounded many Americans over the years and was plotting to kill many more. "He should have been taken out many years ago," he added.

Democratic strategist Jesse Ferguson described foreign policy and national security as a "threshold issue" for Democratic candidates.

"They may not win the race on national security and foreign policy, but they have to pass a threshold of competence, strength and vision that gives voters comfort that they can be commander in chief," he said. "In comparison to Trump, Democrats have an opportunity to look strong and reasonable as opposed to reckless and feckless."

Polls suggest that voters have been unhappy with Trump's leadership on the world's stage throughout his presidency.

Just 35% of voters approve of the way Trump was handling foreign policy back in October, according to a Quinnipiac University poll. Roughly 6 in 10 voters also disapproved of the way he was handling national security and the nation's policy toward the Middle East.

With political risk abounding, Democrats were careful to acknowledge the threat posed by Soleimani as they lashed out at Trump.

Warren called the Iranian general "a murderer, responsible for the deaths of thousands, including hundreds of Americans," though she issued a subsequent statement focusing exclusively on criticizing Trump.

Buttigieg described Soleimani as someone with "blood on his hands from countless operations against American interests," while noting that "taking out a bad guy is not a good idea unless you are ready for what comes next."

As Democrats tried to coalesce around a consistent message, the Republican National Committee pounced, issuing a statement titled "Dems fail first foreign policy test of 2020."

RNC spokesman Steve Guest took a swipe at the entire Democratic field but singled out Biden by name. He noted that the former vice president also opposed the raid that killed Osama bin Laden in 2011.

"At a time when America needs decisive and bold leadership, thankfully President Trump is the one in the Oval Office," Guest said. "What 2020 Democrats offer is a reversal to the failed foreign policy of the past."