Candidates continue off-stage conflicts, and other top moments from the January Democratic debate in Iowa

Six Democrats faced off Tuesday night in the seventh debate of the presidential primary in Des Moines, just weeks before the first-in-the-nation caucuses in Iowa.

All eyes were on the four frontrunners, former Vice President Joe Biden, former South Bend, Indiana, Mayor Pete Buttigieg, Vermont Sen. Bernie Sanders and Massachusetts Sen. Elizabeth Warren, who have been shuffling around in their rankings in recent Iowa polls.

Iowans caucus on Feb. 3 and their decision could help define a narrowing field of candidates. Less than a week later, the candidates will be back on the debate stage Feb. 7 ahead of the New Hampshire primary.

Here are the top moments from the January debate:

Did Sanders say a woman can't win? The conflict continues on stage

The fallout from Massachusetts Sen. Elizabeth Warren's claim that Vermont Sen. Bernie Sanders told her he didn't think a woman could win the White House made an appearance when both were asked about it on stage.

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The alleged comment was made during a December 2018 conversation and sparked a major controversy in the days leading up to the debate, as Sanders has maintained his denial and Warren issued a statement late Monday that in the conversation, "I thought a woman could win; he disagreed."

“As a matter of fact I didn’t say it,” Sanders said during the debate. “How could anybody in a million years not believe that a woman could not become the president of the United States?”

Read more:Elizabeth Warren says Bernie Sanders didn't think a woman could be president. He denied it.

Moderator Abby Phillip appeared not to buy his answer when she turned the question on Warren: What did you think when Bernie Sanders told you that a woman could not be president?

“I disagreed,” Warren said, adding that Sanders is “my friend.”

Warren pivoted the question into an argument for female candidates, repeatedly arguing that women candidates "outperform" male candidates.

“The only people on this stage who have won every single election they've been in are the women,” she said.

The two progressive candidates were also at the center of a clash in recent days over whether Sanders campaign staffers were badmouthing Warren.

More:Elizabeth Warren 'disappointed'; Sanders says the dispute is a 'media blow-up'

In wake of Iran tensions, foreign policy a big issue

The debate moderators put several questions to the candidates on foreign policy in the Middle East, in the wake of the heightened tensions between the United States and Iran after President Donald Trump ordered the killing of a top Iranian general Qasem Soleimani, and Iran responded with missile strikes on Iraqi military bases housing U.S. troops.

Biden argued the United States should return to the nuclear deal that the U.S. and six other countries negotiated with Iran in 2015, that was subsequently pulled out of by the Trump administration in 2018.

“It was working” Biden said.

After the U.S. left the agreement, "we are now isolated,” Biden said. “We have lost our standing in the region. We have lost the support of our allies.”

Buttigieg said preventing Iran from developing a nuclear weapon would be a top priority if he is elected president. But Trump made it harder for the next president to achieve that goal when he withdrew from the Iran nuclear deal, Buttigieg said.

“By gutting that (agreement), they have made the region more dangerous and set off the chain of events we are dealing with” now, Buttigieg said.

Trump recently warned Iran not to pursue nuclear weapons in a public address following the Iranian missile strikes. He said the U.S. was open to negotiating a new deal for peace with Iran, but urged other nations to withdraw from the nuclear agreement.

The Democratic candidates largely agree they oppose Trump’s approach to Iran, but less clear is how their overall approach to the Middle East would be different. Sanders and Minnesota Sen. Amy Klobuchar said they would leave a "small number" of troops deployed in the Middle East, and Biden also said that special forces would still play a role in the region.

“They’ll come back if we do not deal with them,” Biden said of the Islamic State and other U.S. foes in the region.  

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And Warren took a more direct approach: “I think we need to get our combat troops out... keeping combat troops there is not helping.”

Sanders takes shot at Biden over Iraq

Sanders continued his hits on Biden over his stance on the war in Iraq. In recent days, Sanders has highlighted Biden's vote for the Iraq war as a strike against his record.

On stage Tuesday night, Biden acknowledged his vote as a mistake but said that former President Barack Obama opposed the Iraq war, and picked Biden to be his running mate.

“I was asked to bring troops home from that war,” Biden said of Afghanistan.

Biden has previously misstated his support for the war in Iraq; his campaign clarified comments made in a September NPR interview when he claimed he'd been opposed from the beginning.

Former Secretary of State John Kerry, a Biden campaign surrogate, recently said Biden's vote, under the circumstances, "didn't mean you were in favor when the administration made the decision of actually going to war," NBC News reported.

“I think [Sanders] knows full well, as a lot of other people do, that there was a difference in people who felt they needed to give a president the leverage to be able to get Saddam Hussein back to the table, without having to go to war, and that that vote was unfortunately structured in a way that it was sort of either-or,” Kerry said.

Sanders' campaign speechwriter fired back on Twitter, saying that Biden was "rewriting history."

At the debate, Sanders, when asked why his support for war in Afghanistan is different from Biden's vote for war in Iraq, said that the Iraq war was the "worst blunder in modern history." Sanders said he led the opposition to the Iraq war.

How Biden says he'll take on Trump's trash talk

House Speaker Nancy Pelosi is preparing to send impeachment articles against Trump over to the Senate for a trial, where he will likely be acquitted, moderator Wolf Blitzer noted. Since Trump has trashed Biden and his family, will it be harder for the former vice president to run against him, Blitzer asked.

"He has in fact committed impeachable offenses," Biden said, calling hits against his family "irrelevant" to his run against Trump.

“It’s irrelevant,” Biden said. “There’s no choice but for Nancy Pelosi and the House to move."

"Whether the Senate makes that judgment or not, it’s for them to decide," Biden added.

The question, Biden said, is whether or not Trump has done his job.

“He hasn’t done his job,” Biden said, “and it doesn’t really matter whether he has gone after me.”

Biden said he cannot hold a grudge if he’s elected president, even though Trump and the GOP have “savaged” his son, Hunter Biden.

Biden also drew laughter from the crowd when he later said that he has been an object of Trump's affection throughout the campaign, more than anyone else on the stage.

Contributing: John Fritze, Rebecca Morin, Maureen Groppe, Ledyard King and Michael Collins, USA TODAY