Washington (CNN) First things first: The theme song of the week is the theme from The Joy of Painting .

A new Marist College poll finds that 90% of Democrats believe it is a good idea to have a health care system in which there are private insurers and a government option (i.e. public option).

Meanwhile, a smaller 64% of Democrats say it's a good idea to have "Medicare for All" (i.e. a government-run health care plan that pretty much replaces private insurance).

Health care is the top issue for Democratic primary voters, and it has divided the leading Democratic presidential contenders more so than most issues. Sens. Kamala Harris of California, Bernie Sanders of Vermont and Elizabeth Warren of Massachusetts all favor Medicare for All . Former Vice President Joe Biden is the lone top Democrat in favor of the public option , which is the more popular option among Democrats -- and particularly among black Democrats.

The Marist poll is one of a number of polls that suggest Biden has the more popular stance with Democrats (as well as with the general electorate). Our CNN/SSRS poll conducted at the end of last month show the same thing. In that poll, we asked whether there should be a national insurance plan. Among those who said yes, we asked a follow-up: should it replace private insurance?

Among potential Democrats and Democratic leaning independents, 48% favored the public option. This was followed by 31% who wanted Medicare for All. Not surprisingly, just 12% didn't want a national health care plan at all.

Biden is trying to take advantage of these poll numbers. He's now running ads on the fact that his health care proposal allows people to keep their private insurance if they want to.

Biden's backing of the public option may help with one group of Democrats in particular: African Americans. Biden holds a significant lead among them, but Harris was able to eat into that lead following the first primary debate last month. The health care fight allows him to try and win some of that support back by going on the offensive on a major policy issue.

Our CNN poll indicates that the public option is even more popular among black Democrats than it is among Democrats overall. A clear majority, 58%, of black Democrats and Democratic leaning independents want the public option. A mere 23% prefer Medicare for All. No national insurance option at all comes in at 10% with black Democrats and black Democratic leaning independents.

The fact that black Democrats are more favorably inclined toward the public option than the average Democrat makes sense. You can have the public option coexist with Obamacare (Affordable Care Act), which was former President Barack Obama's signature piece of legislation. Black Democrats, in particular, still love Obama. Medicare for All, on the other hand, replaces Obamacare with the goal of covering all Americans through a government health care plan.

I would argue though that African American support for the public option doesn't just have to do with the fact that it's Obama's signature health plan. It's that it's more moderate than Medicare for All. Black Democrats are more moderate than non-black Democrats. Indeed, regardless of race, ideology plays a significant role in determining whether a Democrat prefers Medicare for All or the public option. More moderate Democrats prefer the latter.

The Medicare for All vs. public option fight is, in this way, a representation for one of the reasons of why Biden is doing so well with black voters. While some of his appeal almost certainly has to do with his service under Obama, Biden (at least in labeling) is ideologically closer to black voters than the other Democrats. He's the only moderate in the top tier. Biden does better among moderates overall, which helps him significantly with the predominantly moderate African-American voting bloc.

If Biden continues to be able to successfully make the pitch that he is a better fit ideologically on important issues such as the public option, it is likely to help him maintain his overall lead in the primary.