(CN) – Former Vice President and Democratic presidential front-runner Joe Biden excoriated President Donald Trump on Tuesday, calling the president’s approach to Iran erratic, devoid of strategy and not fully explained to the American people.

“President Trump has no strategy here, no endgame,” Biden said in a terse speech delivered in New York. “His constant mistakes and poor decision-making have left the United States with a limited slate of options moving forward. And most of those options are bad.”

Biden is referring to the killing of General Qassem Soleimani – head of Iran’s Quds Force, the foreign-operations branch of the Islamic Revolutionary Guard Corps. Trump ordered Soleimani’s assassination in retaliation for an attack on the U.S. embassy in Iraq and other acts of aggression by Iranian militias in the Middle East.

Biden agreed such acts needed to be countered forcefully by the United States, but said killing one general who was particularly revered in Iran was an unnecessary escalation that thrust the United States to the brink of a costly war.

“There is a smart way to counter Iran and a self-defeating way,” Biden said. “And Trump’s approach is, in my view, demonstrably the latter.”

Biden also alluded that the smarter, more restrained way to approach Iran was exemplified by the Iran Nuclear Deal, cinched by President Barack Obama and other European allies while Biden was serving as vice president.

“When we had the Iran deal, we had verifiably cut off every one of Iran’s pathways to a nuclear weapon,” Biden said. “One of the greatest threats to stability in the region and global security was off the table.”

Biden argued much of Trump’s foreign policy, including alienating close allies in Europe, has weakened the United States’ position on the global stage.

“We are alone,” Biden said. “At this most dangerous time when we should be rallying our allies, President Trump’s ‘American First’ dogmatism has come home to roost.”

Members of the Trump administration appeared on several cable news programs to make the case that Soleimani was a terrorist who had the blood of Americans on his hands. They argued the response was proportional, done to stop imminent attacks and indicated they were committed to de-escalating tensions with Iran rather than clamoring for war.

“It’s the right decision, we got it right, the Department of Defense did excellent work,” Secretary of State Mike Pompeo said during a Tuesday morning news conference.

But Trump has been noticeably absent, declining to make any speeches or addresses on the matter. Instead, he has been communicating through his preferred medium of Twitter, where he has threatened to escalate hostilities should Iran retaliate.

Biden criticized Trump’s lack of accountability and his perceived refusal to work with Congress on forming a unified strategy.

“Mr. President, you have to explain your decision and strategy to the American people,” Biden said.

Biden clearly used the moment to burnish his foreign policy credentials, alluding to his time in the White House and his experience with both the executive and legislative branches.

The speech comes at a time when Biden appears to be solidifying his lead in both states that hold early primaries and nationally.

A Morning Consult poll released Tuesday saw Biden with a commanding lead on the rest of the field, a full 8% in front of Sen. Bernie Sanders, who occupied second place.

A poll in Iowa on Sunday found a dead heat, a marked improvement for Biden who was formerly trailing in the pivotal state. Biden has spent considerable campaign capital in terms of time and money in the Hawkeye State.

Sanders also used the tensions with Iran to show a distinction with Biden, attacking him on his record during a recent interview.

“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 told CNN’s Anderson Cooper on Monday evening.

It is rare for Sanders to attack his fellow Democrats on the campaign trail, but criticizing Biden by name shows an increasing awareness that the vice president’s lead in the polls has remained steady throughout the early stages of the process.

The primary season is approximately a month away, with the Iowa Caucus slated for Feb. 3.