A recurring theme in the post-election GOP hand-wringing of 2008 and 2012 is that the party failed to nominate someone with broad appeal across all Republican constituencies. So one big question heading into 2016 is which candidates might be able to solve that problem and enter the general election in better position to broaden their support.

With that in mind, the Wall Street Journal has some interesting results from a poll question about which of 14 potential GOP contenders the party's primary voters could or could not see themselves voting for.

You can see the results to the left. At first glance, the green "could support" numbers show a tight race, which is almost certainly true. But the difference between those numbers and the gray "could not support" numbers tell us something about which candidates might be best-positioned to solve the previous problem of party unity.

Taking the net number of the "could" minus the "could not," the leaderboard looks rather more stratified:

2. Marco Rubio, +30

3. Ben Carson, +23

4. Mike Huckabee, +12

5. Bobby Jindal, +11

6. Rand Paul, +9

7. Jeb Bush, +7

Put that way, there's a significantly larger gap between Walker and Rubio at the top and, say, Paul and Bush. At minus-25, matters would also seem rather hopeless for Chris Christie, who once looked like a formidable future candidate.

But today's numbers don't necessarily tell us much. After all, 30 percent of respondents didn't voice an opinion about Walker; 41 percent abstained when asked about Carson; for Jindal, it was 39 percent. The gap tends to close as more voters voice an opinion about a particular candidate, which is what you'd expect. So what might things look like as voters form opinions?

There obviously are a myriad of permutations, and an accurate forecast is impossible. But for illustrative purposes I chose three possibilities: a scenario where two-thirds of undecided* voters decide they can't back any of the candidates (e.g., after an especially negative campaign); a scenario where undecided voters split evenly; and a scenario where two-thirds of undecided voters decide they can back any of the candidates (e.g., after a more positive campaign). For the purposes of the chart below, I've left off Donald Trump, Lindsey Graham and Christie, who remained in the bottom three in all scenarios, as well as Rick Santorum, who didn't break into the top half in any scenario.

Keeping in mind that these rankings illustrate how unified the party might be behind a particular candidate, not which candidate is most likely to win, a few things jump out:

Walker and Rubio finish at the top of all three scenarios. (So does Carson, but I don't consider his chances as serious as the others'.) Among the others, only Jindal ever breaks the 60 percent threshold. And Paul, Bush and Huckabee -- three candidates about whom almost all voters already have formed opinions -- fare best, relatively to the others, if the campaign is more negative. That's especially interesting regarding Bush, who has so far presented himself as a more positive, ideas-centric person. Perry, Cruz and Fiorina seem highly unlikely to galvanize the base.

It will be interesting to see how these numbers change as voters familiarize themselves with the candidates. But it would seem that the ceiling as of now is highest for Rubio and Walker, especially if they can avoid being dragged down into a messy political brawl of a primary.

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*Undecided refers to the voters who didn't voice an opinion about each particular candidate. The number varies from candidate to candidate.