Warren's success depends on her answering these five questions

Sen. Elizabeth Warren's stock is rising in the presidential race. The Massachusetts Democrat has soared in polls and now comfortably occupies second place in a number of them, including the latest Fox News survey, and in the Real Clear Politics poll average.

It's too early to pull the final curtain down on Sen. Bernie Sanders, I-Vt., but his supporters are fleeing and he's got nothing to lure them back from Warren or to entice other voters to take a look at him. Of the top four candidates (Warren, Sanders, Sen. Kamala Harris and former vice president Joe Biden), he looks the weakest at this juncture.

Warren's success has not yet brought her in shouting distance of Biden in national polls or early state polls. A huge chunk of the primary electorate hasn't been paying much attention, let alone settled on a candidate. I can think of at least five questions, the answers to which may tell us whether she's primed to knock out Biden and become the favorite for the nomination.

First, can she campaign from the heart as well as from the head? She's got plenty of plans, more plans than the other contenders combined. Warren arguably has established herself as the wonkiest candidate in this race, or perhaps any race. But Hillary Clinton had plans, too.

What Clinton lacked and Warren hasn't yet shown is the ability to connect viscerally with the audience, deliver the soaring rhetoric many Democrats like to hear and show some heart on her sleeve. If you compare her rhetoric to Biden's or Beto O'Rourke's or Sen. Cory Booker's soon after the El Paso, Texas, shooting, all three of them sounded more emotional and "presidential."

Second, can she show she can manage President Trump? The absurdly irrelevant Native American DNA issue lingers because it suggests Trump can push her around and put her on defense before she even gets to general election. There are a few ways to deal with this. She could ignore him. She could pummel some other Democrat to show her toughness (but she'd better not pick Biden, as Harris found out) without raising the ire of voters who don't want infighting.

Another way would be to go on offense, in ways that get under his skin just as Biden manages to do. I don't suggest she start throwing Twitter bombs at him, but she'd do well to mock him now and then.

A president who thinks he might buy Greenland, thinks Kim Jong Un has eyes for only him, acts like Vladimir Putin's lap dog, still hasn't passed Trade 101 and hires the bottom of the barrel deserves a good tongue-lashing now and then. More seriously, she can go after him for his racist incitement. A majority of Americans, according to the aforementioned Fox News poll, already blame to some extent the sentiments Trump has expressed for recent mass shootings. Show voters now that she can go for the jugular, and she would stomp out the last embers of "unelectable" talk.

Hitting him effectively on something like this will give voters confidence in her sparring abilities and also underscore that Trump's own taunts are pathetically small and juvenile.

Third, can she navigate the health-care issue? Sanders, the only other top-tier candidate who backs single-payer health care, is sinking and won't provide much cover the next time all the other candidates start whacking away at Medicare-for-all.

Warren to date conspicuously has not put out her own health-insurance plan, although that gives her one more shot at taking the single-payer target (in the general election) off her back. Once upon a time (like this past spring), she sounded amenable to public-option ideas as initial steps toward Medicare-for-all.

Perhaps, as Harris smartly did, she can come up with a political off-ramp to respond to concerns such as how to transition to such a system, its exorbitant cost and its potentially low reimbursement rates for doctors and hospitals that could threaten to create shortages especially in rural areas.

Fourth, can she hold up under fire as a front-runner? Once all the candidates are focused on knocking her off stride, we'll see if she can keep her cool, avoid looking defensive and substantively respond to legitimate critiques from moderates about her programs. One major line of attack is that her plans (e.g., student-loan forgiveness) aren't necessarily focused on the neediest Americans or working-class people (many of whom don't go to college), who as taxpayers would in effect subsidize richer Americans' health care, college education and more. Another attack she should expect will focus on her wealth tax that has plenty of issues (e.g., moving assets overseas) and is unlikely to provide the money she'll need to pay for everything. She's going to have to level with voters about the prospect of taxes on people who aren't super-duper rich.

Fifth, can she pass the commander in chief test? With the exception of Biden, this poses a challenge for all the presidential contenders. They've all got to show not only a mastery of the issues and the ability to critique Trump (that part is easy) but the ability to articulate a vision that doesn't devolve into the left's version of retrenchment.

Explaining how she is going to lead the United States on the world stage and confront a dizzying array of threats will be essential to winning the nomination.

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