Bernie Sanders has a very clear theory of what is wrong with Hillary Clinton: She is less left-wing than he is. She is less of a conviction politician, less politically daring, less consistent in her record, and more beholden to interests that benefit from the status quo. Agree or not, that's what he's saying. You don't need to agree with it or intend to vote for him to understand it and be able to repeat it coherently.

Clinton, by contrast, is all over the map.

This was on clear display Thursday night at the final Democratic debate before the New York primary on Tuesday night. Sanders has improved his range as a debater, and across a variety of subjects and questions he hammered home his basic point painting his preferred picture of Clinton. Clinton herself continues to have impressive command of the issues, but seems to have only the haziest notion of what she wants to say about Bernie Sanders, delivering a mixed message with no clear takeaway or big moments.

The good news for Clinton supporters is that she has an enormous lead at this point anyway, and the aversion to stark choices that makes it hard for her to develop a compelling line of attack would likely serve her well as president.

Clinton's lines of attacks often contradict

It's not that she has no message against Sanders, it's that she has almost too many anti-Sanders messages. A flurry of jabs from all directions that often sting a little, but rarely truly draw blood. Most of them are true, or at a minimum defensible, but it's often not exactly clear what they amount to.

At times, Clinton says (accurately) that Sanders's ideas are politically unachievable and electing him to the White House will not actually lead to his legislative proposals being enacted.

At times, Clinton says (accurately) that Sanders's ideas are not based on rigorous financial accounting and probably couldn't be paid for in exactly the way his campaign has said.

At times, Clinton says (accurately) that Sanders is not as personally well-versed in policy details as she herself is.

These are all true statements, and to the extent that you find any one of them to be overwhelmingly compelling, throwing all of them at Sanders does the trick. But they also tend to undermine one another.

Given that Sanders's ideas are not going to secure majority votes in Congress, for example, what possible difference does it make that the pay-fors don't add up correctly? And how egregious a sin is this when Sanders is clearly not that personally interested in the details of policy? Pondering the flurry of attacks ultimately tends to push one up to the higher levels of abstraction where Sanders is more comfortable. Isn't it true that, in principle, if Canada and the United Kingdom can secure universal health insurance provision at a lower per capita cost than the United States, then we should be able to also?

The value of sticking to a line

Back in 2012, Barack Obama decided to run against Mitt Romney as an out-of-touch Richie Rich whose hard-right economic agenda would devastate the American middle class. He didn't call Romney a flip-flopper, even though there are lots of good flip-flopper attacks on Romney, because calling him a flip-flopper would undermine the idea that he's a hard right ideologue.

Clinton doesn't show this discipline, time and again hitting Sanders from the left on guns even while she hits him from the right on most everything else. Sometimes she says she essentially agrees with him, but that her plans for achieving their shared goals are more realistic.

But a campaign needs to define its opponent — to tell a simple story about why someone shouldn't vote for him or her. And together, all these arguments from Clinton end up sounding like a muddle. They don't paint one clear picture of Sanders — indeed, they often contradict each other. Is he too liberal, not liberal enough, or just as liberal as Clinton?

Clinton had a coherent message, but she dropped it

The strange thing is that back on February 11, I agreed with my colleague Andrew Prokop that Clinton had finally found her message: "I am not a single issue candidate, and I do not believe we live in a single issue country."

That is a message on which Clinton could hang most of her critiques of Sanders:

Sanders has been soft on guns, not because he's in the pocket of the NRA but because it's an issue that can't be easily assimilated into his class warfare worldview.

Sanders voted against the 2007 immigration reform bill, not because he hates immigrants but because his passion for anti-business causes trumped other concerns.

Sanders's ideas on health care might make sense in principle, but insisting on reopening this fight would prevent other issues from getting on the agenda.

Sanders's relentless focus on a single big idea about crushing corporate power prevents him from seeing that when you sit in the Oval Office it actually matters whether you get the details right.

Sanders's self-righteousness about fundraising is going to make it impossible for him to build legislative coalitions and make even incremental progress on even his core issue.

The point would be not that Sanders is a bad guy or that his idea is wrong or even that he's a bad senator, but that he belongs in the Senate, which is an ideal vantage point from which to flail away at one big idea. The presidency requires a fox, not a hedgehog, and that means Clinton.

Clinton rode a version of this "not a single issue candidate" message to a series of victories in Nevada, South Carolina, Massachusetts, and much of the South. But she seems to have gotten spooked by her unexpected loss in Michigan, where the toxic lead in Flint had appeared to be an excellent example of America not being a single issue country. We haven't heard much about it since early March, and in Thursday night's debate she was all over the map.

Clinton's muddled message reflects her greatest strength

The good news for Clinton is that she already has a giant lead in delegates and is well ahead in the polls in New York. She is overwhelmingly likely to be the Democratic nominee, and is likely to enjoy the good fortune of running against Donald Trump or Ted Cruz in November rather than one of the dozens of incumbent GOP governors or senators who would be harder to beat.

The good news for America is that while running a campaign bears some resemblance to running a presidential administration, they're really quite different. And Clinton's tendency to develop an unclear message is directly related to one of her greatest potential strengths in office.

Clinton is an absolutely first-rate synthesizer of diverse ideas and perspectives. Whether she's talking about who should split the check on a date or doing a better job than Bernie Sanders of explaining Bernie's bank breakup plan, she is really good at understanding what other people are saying and mashing various ideas up together. Presented with multiple credible options, she doesn't choose — she combines and remixes.

This is a bad way to write a stump speech, and a terrible way to plow through a 120-minute debate. But it's a pretty good way to govern. Especially in a country like the United States with a cumbersome legislative process, a high degree of decentralization, and enormous domestic diversity.

Sanders is right to say that the successes of the Obama administration have been frustrating, partial, and often conceptually incoherent compared to some models available abroad. But things turn out this way for a reason — and the reason is the nature of American political institutions, not the details of campaign finance. Sanders won't be able to change the messiness of American policymaking no matter how hard he tries, and the very "say yes to everything then sand off the edges" instinct that makes Clinton's hits on Sanders so weak will serve her well in dealing with it.