WASHINGTON — Waging a presidential campaign amid rising tensions with Iran 12 years ago, Joe Biden, then a senator from Delaware, had a warning for President George W. Bush should he decide to take military action without congressional authorization.

"I want it on the record, and I want to make it clear," Biden said. "If he does, I will move to impeach him."

Now Biden is the Democratic front-runner in the polls to take on President Donald Trump, and the potential for a clash with Iran is once again growing. On Thursday, the former vice president warned that the Trump administration’s strategy is a “self-inflicted disaster” that has made war more likely — and his campaign says his view on potential impeachment hasn’t changed.

In a statement issued Thursday, hours after reports that a U.S. drone was shot down over the Strait of Hormuz, Biden said the administration’s withdrawal from the Iran nuclear deal negotiated in the Obama administration has precipitated the current crisis.

“Another war in the Middle East is the last thing we need,” he said. “Make no mistake: Iran continues to be a bad actor that abuses human rights and supports terrorist activities throughout the region. But what we need is presidential leadership that will take strategic action to counter the Iranian threat, restore America's standing in the world.”

Separately, the campaign said that Biden believes war against Iran without specific congressional authorization “would be unconstitutional."

"An illegal war that puts at risk thousands of American lives and would bog down the U.S. military in conflict in the Middle East for years would certainly qualify as an impeachable offense,” Biden spokesperson T.J. Ducklo said in a statement to NBC News.

Biden's 2007 comments, made at a New Hampshire town hall meeting as he was running for president, made it clear he was prepared to take the extraordinary constitutional step against Bush over Iran. But his broader view of impeachment was otherwise one of restraint, grounded in both his view of constitutional law and the political reality at the time.

And the argument he laid out then perhaps offers the best view of how he sees the question now, particularly as his party grapples with whether to escalate its constitutional clash with Trump in the wake of special counsel Robert Mueller’s report on Russian election interference.

At the town hall meeting in Portsmouth, just more than a month before the 2008 New Hampshire presidential primary, Biden raised impeachment in response to a voter who said he was worried that Bush would launch strikes against Iran and asked what he would do if he was the Democratic nominee.

Biden, referring to one of his primary rivals, said, "I'm not Dennis Kucinich saying impeach everybody now," according to NBC News video of the event.

"But let me tell you, I have written an extensive legal memorandum with the help of a group of legal scholars" he said. "The president has no authority to unilaterally attack Iran."

Later, another voter pressed Biden about why he wouldn’t move forward on impeachment immediately, over a variety of then-contentious issues including the firing of seven U.S. attorneys, "as a signal to the world."

Biden said it was "arguable constitutionally" whether Bush had at that point taken actions that had risen to the level of high crimes and misdemeanors. He also said it could be "counterproductive" to initiate impeachment proceedings against Bush, noting that as a U.S. senator he had served during two other impeachment inquiries — against Richard Nixon, right after Biden arrived in the Senate, and Bill Clinton.

In 2007, Biden argued that "the American people would judge us very harshly" if Congress launched an impeachment process — without a major precipitating event like military action in Iran — when Bush had just 15 months left in office. He also noted that then-Vice President Dick Cheney would be next in line, saying: "If you're gonna impeach George Bush you better impeach Cheney first. Not a joke."

Americans "want us to get about the business of trying to figure out how to make an accommodation, make compromise, reach conclusions, practical, pragmatic solutions to some of the problems we have," he said then. Instead of impeachment, traditional congressional oversight by the new Democratic majorities in the House and Senate could "begin to seek through subpoenas, records before they're destroyed, determining whether or not there are criminal acts that have been in fact engaged in."

"If it turned out that the evidence showed that they were, then we should criminally prosecute these men and women when they leave office," Biden said.

But the threat of impeachment against Bush on Iran could itself be useful, Biden argued.

"I think the best deterrent is for the president to know, even at the end of his term, we would move and move to follow through with that so his legacy would be marred for all time if he acted in what was clearly, clearly an impeachable offense," he said.

Today, Biden often sounds closer to Speaker Nancy Pelosi than to one of his 2020 rivals, Sen. Elizabeth Warren, D-Mass., when it comes to impeachment, again casting it as a constitutional option of last resort.

Speaking in Concord, New Hampshire, two weeks ago, Biden was again asked about impeachment. He began by again arguing that the Trump administration needed to cooperate "with the legitimate investigations of the Congress." If he did not, "then, in fact, the Congress has no option but to begin an impeachment inquiry. Because under an impeachment inquiry they have more power to be able to demand and subpoena."

“I am not looking forward to an impeachment process,” he added. “I really mean it, I think it will be a gigantic distraction on things that we should in fact be focusing on getting done. The truth of the matter is, though, that there is a constitutional obligation. My job is to impeach him a different way. Beat him."