With less than a month to go until the Iowa caucuses, Sen. Bernie Sanders of Vermont is seizing on the killing of Iran’s top military general as a way to target top 2020 Democratic nomination rival Joe Biden over his support for the Iraq War nearly two decades ago.

It's just one indication of how President Trump’s order last week for an airstrike that killed Qassem Soleimani has transformed the Democratic nomination race – at least for now – by putting the spotlight on foreign policy and national security.

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Sanders has been eager to repeatedly weigh in the past five days, using the attack to highlight how his anti-war credentials differ from the former vice president's record.

“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 Monday night in an interview on CNN.

It’s a line the populist independent senator has used over and over since Biden jumped into the race last April, but with tensions rising in the wake of the attack, there’s more urgency to Sanders’ message.

Sanders appears to be drawing a clear line between himself and Biden – who as a senator from Delaware and long-time Foreign Relations Committee member in 2002 voted to authorize military action in Iraq. Sanders, a member of the House of Representatives at the time, opposed the measure.

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The crisis with Iran, at the same time, gives Biden the chance to showcase his decades of foreign policy experience in the Senate and as vice president under President Obama.

Campaigning in Iowa this past weekend, Biden emphasized that Americans need “a president who provides a steady leadership on Day One.”

And Biden stressed last week during a stop in New Hampshire that “I’d put my foreign policy experience against anyone in the country right now.”

But his Iraq War vote from nearly two decades ago complicates matters. And Sanders' repeated jabs at Biden’s vote are seen as a way to undercut the former vice president in an arena that’s supposed put him leagues above his nomination rivals.

On Tuesday, Biden took aim at Trump over the escalating crisis with Iran – blaming the GOP incumbent for ripping up the nuclear deal signed with Tehran during the Obama administration.

“The seeds of dangers were planted by Donald Trump himself on May 8, 2018 – the day the president tore up the Iran nuclear deal, against the advice of his own top national security advisers, the day he turned his back on our closest European allies,” Biden said in New York City.

Former South Bend, Ind., Mayor Pete Buttigieg is the only one of the top-tier contenders who served in the military. He did a tour of duty in Afghanistan as an intelligence officer in the U.S. Naval Reserve.

The candidate repeatedly spotlighted his service as he campaigned in New Hampshire in the days following last week’s attack.

Asked by Fox News on Friday if his time on the ground in a war zone gives him a leg up on his rivals, Buttigieg answered that “it’s certainly useful experience.”

Pointing to his own experience in Afghanistan, he noted that “when it was a U.S. policy that sent you into a warzone, you think about the ramifications and the seriousness of decisions made in the Situation Room differently. And I also think it can’t hurt to have some familiarity with the issues on the ground.”

Like Sanders, Buttigieg has also targeted Biden over his Iraq War vote – spotlighting two weeks ago that the vote was the nation’s “worst foreign policy decision” of the 37-year-old candidate’s lifetime.

“This is an example of why years in Washington is not always the same thing as judgment,” Buttigieg added during a recent interview with Iowa public television.

Biden responded by saying “I’m very proud of my record and...I’m delighted to debate foreign policy with my friend.”

That opportunity will come next Tuesday in Iowa – at the next Democratic presidential primary debate.

Biden, Buttigieg, Sanders and Sen. Elizabeth Warren of Massachusetts will be on that stage – as will Sen. Amy Klobuchar.

On Tuesday, the Minnesota Democrat also indirectly took aim at Biden.

Speaking with reporters on the campaign trail in New Hampshire about the rising tensions with Iran, Klobuchar explained that “I was against the Iraq War and actually it was a major issue in my campaign the first time I ran for the Senate because the congressman on the other side of me – he supported it.

“I think some people weren’t looking at evidence. I think it’s important to look at evidence,” she added, in what appeared to be a jab at the former vice president.

The attack has radically changed coverage of the campaign trail – and put national security front and center with just a month to go until voters finally get to weigh in.

A veteran political scientist sees this as a challenge for the candidates.

“It’s a big test for all of the campaigns because they have been very comfortable talking about domestic issues in every debate and at town halls. They’ve been very much focused on the same ground,” noted Wayne Lesperance, vice president of academic affairs at New England College. “Now we’re in new territory and we’re going to see if these folks have real foreign policy chops.”