Six presidential candidates take to the debate stage Tuesday night, less than three weeks before the Iowa caucuses and before the start of the impeachment trial, which could keep the three sitting senators tied up in Washington. Especially for the latter group — Sens. Bernie Sanders (I-Vt.), Elizabeth Warren (D-Mass.) and Amy Klobuchar (D-Minn.) — this might be the final and most significant opportunity to impress caucus-goers, a large percentage of whom are undecided or still open to persuasion. All the candidates have their work cut out for them.

Former vice president Joe Biden: Biden needs to capitalize on his standing as the only ready-from-day-one commander in chief. That is the subject of a new ad:

What he does not want to do is argue about his Iraq War vote or NAFTA vote with Sanders. He can try dismissing Sanders as “desperate” or “attacking everyone,” but the easiest way to defuse that line of attack is to cite his eight years of foreign policy experience at President Barack Obama’s side. Beyond that, he will want to make the case that general-election voters are not going to feel comfortable with a socialist and someone who propounds the left’s version of President Trump’s retrenchment philosophy.

Since the Iowa Democratic caucus voters seem truly concerned with electability, that is an argument Biden should pound home (arguing there is no poll in which anyone performs better than he does in a face-to-face match-up against Trump), as he does in this ad:

Sanders: The senator is likely to face incoming fire from all directions. His biggest problem will be handling Warren’s accusation that he told her in a private meeting that a woman could not win. He dare not call her a liar. Worse would be saying she was “confused.” Worst of all would be allowing his telltale temper to show.

From Biden, he is likely to get “It’s not women; it’s the socialist who cannot get elected.” If Sanders doubles down on his “Out of the Middle East” line or cannot discuss foreign policy in any depth, he will confirm that he is not a credible commander in chief and hence, not electable.

Biden, Klobuchar and former South Bend, Ind., mayor Pete Buttigieg might hit him on Medicare-for-all and his fixation with pie-in-the-sky spending plans. As Ronald Brownstein points out, Sanders’s new spending adds up to at least $60 trillion over 10 years, doubling what we would otherwise spend on the entire federal government (including $34 trillion for Medicare-for-all, $16.3 trillion for the Green New Deal, $2.5 trillion on housing, $1 trillion on infrastructure, $2 trillion on free college and eliminating student debt, $7.5 trillion for a job guarantee plan and $1 trillion for K-12 education). Sanders’s tax plans would cover only 40 percent to 45 percent of the cost of the new spending, making Trump seem conscientious about the debt. (“Sanders’ plan would translate into a roughly 20 percentage point increase in federal spending relative to the economy. ... Measured as a share of the economy, then, Sanders is proposing spending increases about 15 times larger than [President] Obama ran on in 2008, and roughly 30 times as large as [Hillary] Clinton’s in 2016.”)

Warren: This is her best chance to reverse her slide in the polls, take back a share of progressive voters from Sanders, play to female voters and present herself as far more electable than Sanders. This was where she hoped to position herself all along, before getting caught up in defending a Medicare-for-all plan that was not even central to her overall message.

Without necessarily calling Sanders a liar for denying his remark about women’s electability, she should feel free to show some righteous indignation over a bunch of white guys telling Democrats that a woman is too “risky.”

She otherwise may want to stay largely positive in contrast to her ineffective scuffling with Buttigieg over fundraisers in the last debate. Given the start of the impeachment trial, she may not have many more chances to directly face Iowa voters before the caucus. Hammering home her central message (i.e. un-rig the government to work for the middle class) therefore may be her top priority.

Buttigieg: As Warren and Sanders point fingers while Sanders and Biden fight over votes a decade or two ago, Buttigieg has the perfect opportunity to say: Aren’t you sick of these Washington politicians bickering about stuff that doesn’t touch your life? No wonder nothing gets done there.

Buttigieg can offer himself as a young, fresh-faced moderate — a problem-solver without baggage and a veteran who is going to run circles around Trump in the general election. He can set himself apart both from Biden (on Iraq) and the two uber-progressives who want to pull all troops out of the Middle East with little understanding of the consequences.

Given Trump’s ever-intensifying crazy, inappropriate and unhinged conduct (e.g. lying about the basis for a reckless military strike, painting Democratic leaders as terrorist-lovers), Buttigieg’s vision of a president who, when he comes on TV, lowers your blood pressure rather than increases it, could sound awfully attractive.

Klobuchar: She would be wise to remind Democrats they can have it all with her — someone with more experience than Buttigieg, a better track record than Warren and Sanders on getting things done across the aisle, a more electable Midwesterner than Buttigieg (who did not win at the state level) who has won in red districts, a ready commander in chief (who traveled the world with then-Sen. John McCain, but without the vote on the Iraq War) and a woman who will drive Trump nuts, just like House Speaker Nancy Pelosi (D-Calif.) does. Like Buttigieg, she can afford to let the squabble play out, although she is likely to bolster Warren’s argument about women’s electability, implicitly tagging Sanders as a grumpy old sexist.

Tom Steyer: He should explain why it is a good idea for a white male billionaire (who was able to swamp the airwaves to raise name recognition and spend like crazy to round up the required number of donors) to be onstage while a slew of more experienced, diverse candidates are not. His notion that we need a businessman (!) to run for president, going back to the now thoroughly debunked notion that government can be run like a business or that business experience is a substitute for public service, might prompt some snickering.

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