While that made for compelling television, it also distracted from a starker ideological choice that looms for Democratic voters in the weeks ahead.
The more substantive portions of the two-hour debate at Drake University in Des Moines put in stark relief the chasm between the approaches of Sanders and Joe Biden - the two leaders in Iowa and national polling - on the biggest issues that face a president, including foreign policy, health care and trade.
It also highlighted continuing tensions between the two men over experience vs. judgment, incrementalism vs. radicalism and whether Democrats are more likely to win in November by igniting the base or appealing to disenchanted moderates who defected to Donald Trump in 2016.
Whomever is coronated at the convention in Milwaukee six months from now will chart the future of the party as its standard-bearer. In Sanders' case, he has spent decades proudly resisting pressure to register as a Democrat. He remains an independent who caucuses with the Democrats in the Senate.
Iowa looks like a jump ball, with the latest polls showing no overwhelming favorite and many voters either undecided or willing to change their minds. The next three weeks would be an unpredictable free-for-all in the Hawkeye State anyway. But the impeachment trial threatens to strand a handful of senators in Washington for days at a time with only Sundays away from the chamber.
It is conceivable that neither Biden nor Sanders ultimately wins the Feb. 3 caucuses. Nevertheless, the two septuagenarians represent the ideological goalposts and the outer bounds - Sanders on the left and the Biden on the right (which, to be clear, is still left-of-center) - of what party regulars will abide.
"Joe and I have a fundamental disagreement here, in case you haven't noticed," Sanders said last night during the round on trade, a salient issue in a farm state where children are taught in school that Iowa is a net exporter. The line, though, can be applied to most every other flashpoint in Democratic politics.
Just as he opposed the North American Free Trade Agreement, which Biden voted for, Sanders now opposes its replacement, the U.S.-Mexico-Canada trade deal. This iteration just passed the Democratic-controlled House and won the endorsement of the AFL-CIO. It's awaiting a vote in the Senate. "The answer is we could do much better than a Trump-led trade bill," Sanders said. "If this is passed, I think it will set us back a number of years."
Biden, who supports the new deal, accused Sanders of knee-jerk opposition to everything. "I don't know that there's any trade agreement that the senator would ever think made any sense, but the problem is that 95 percent of the customers are out there," Biden said, referring to the rest of the world. "So we better figure out how we begin to write the rules of the road, not China."
Sanders attacked Biden for voting to ratify multiple agreements over the years that he said have helped large multinational corporations at the expense of workers. Biden compared Sanders' approach to "poking our finger in the eye of all of our friends and allies" by not trying to negotiate trade agreements with the rest of the world, which he argued empowers China.
The trade clash was particularly interesting to watch because Sanders proudly stood alone onstage among the top-tier candidates in opposing the USMCA deal. Pete Buttigieg, Amy Klobuchar and even Warren endorsed it. Trying to show that she has a pragmatic streak, Warren called the deal imperfect but reasoned that "it will give some relief" to farmers and workers. "We get up the next day and fight for a better trade deal," she said.
It was a reminder of the extent to which the other candidates have all sought to position themselves somewhere between the poles of Sanders and Biden, and this played out repeatedly. In theory, Biden and Sanders occupy separate "lanes," to use the parlance of the operative class. But both men see the other as a direct threat. The Sanders team, in particular, has believed all election cycle that they're competing for Biden voters just as much as Warren voters.
Warren also tried to distinguish herself at one point by noting that she was the only candidate onstage who has defeated a Republican incumbent in the last 30 years. She ousted Republican Scott Brown in 2012 to take back Ted Kennedy's Senate seat in Massachusetts. Sanders chimed in to say that he defeated a GOP incumbent in Vermont to win a House seat in 1990. An amused Warren, once a high school debate state champion in Oklahoma, noted that this was why she specified 30 years. Then Biden added that he won a major upset in 1972 - 48 years ago - over a Republican incumbent to win his Senate seat.
Biden often sounds like he's promising a return to the pre-Trump status quo, when he was vice president. "We can overcome four years of Donald Trump, but eight years of Donald Trump will be an absolute disaster and fundamentally change this nation," he said. "We have to restore America's soul, as I've said from the moment I announced."
Sanders counters that "this is the moment when we have got to think big, not small": "This is the moment when we have got to have the courage to take on the 1 percent, take on the greed and take on the corruption of the corporate elite," he said in his closing, "and create an economy and create a government that works for all of us, not just the 1 percent."
CNN's Abby Phillip also noted that Sanders identifies as a democratic socialist and pointed to a poll that showed about two-thirds of Americans don't like the idea of voting for a socialist. She wondered, "Doesn't that put your chances of beating Donald Trump at risk?" Sanders replied, "Nope, not at all." He pivoted to attack Trump, displaying the moral certitude that his supporters love but Democratic establishmentarians loathe.
The gulf between Sanders and Biden was apparent from the opening question of the debate. The crisis in Iran has prompted the leading candidates to re-litigate the 2002 debate over whether to go to war with Iraq. "Joe and I listened to what Dick Cheney and George Bush and [Donald] Rumsfeld had to say," Sanders said. "I thought they were lying. I didn't believe them for a moment. I took to the floor. I did everything I could to prevent that war. Joe saw it differently."
Biden emphasized his work bringing troops home from Iraq as Barack Obama's vice president. "It was a mistake to trust that they weren't going to go to war," he said, referring to the Bush administration. "They said they were not going to go to war. . . . It was a mistake, and I acknowledge that."
The well-trod debate over health care was similar, as Biden and Sanders went at it again over the price tag for Medicare-for-all and the other candidates staked out ground in between them. Phillip, one of three moderators, asked Sanders about a study that said his policy proposals would double federal spending as a share of GDP to a level not seen since World War II. "No, my plan would not bankrupt the country," he answered. "I think you should show how you're going to pay for things, Bernie," replied Klobuchar.
Warren sponsored Sanders' Medicare-for-all bill, but she moved away from it in the face of questions about how she'd implement it without raising taxes on the middle class or kicking people off their private insurance. Warren ultimately proposed a three-year transition period to Medicare-for-all, but this only led to attacks from her left and right. Last night, Warren and Buttigieg bickered about who would get covered and how much it would cost.
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