Sen. Elizabeth Warren (D-Mass.), left, and then-Secretary of State Hillary Clinton talk during a Senate Foreign Relations Committee nomination hearing in Washington, D.C., on Jan. 24, 2013. (Andrew Harrer/Bloomberg)

The Democratic Party has renewed its focus on income inequality, hoping to ride a populist wave to a third straight term in the White House in 2016. In fact, it was the prevailing focus of Hillary Clinton's campaign launch. She said in her announcement video that the "deck is stacked" in favor of those at the top -- echoing the tone of Sen. Elizabeth Warren (D-Mass.).

And there's good reason for this message: Poll after poll shows a huge majority of Americans are concerned about income inequality. A recent Washington Post-ABC News poll showed 83 percent of Americans say the wealth gap is a problem -- including 51 percent who call it a "major problem." Gallup just this week showed that just 31 percent of Americans think wealth is fairly distributed.

But another new poll suggests that the income inequality argument has its limits. The NBC News/Wall Street Journal poll asked Americans which concerned them more:

  1. The income gap between the wealthiest Americans and the rest of the country
  2. Middle and working class Americans not being able to get ahead financially

In total, 28 percent chose No. 1 -- the income inequality argument -- while 65 percent chose No. 2.

This isn't a totally new finding. A 2011 Time/Abt SRBI poll found 34 percent said it's "more important to reduce inequality in income and wealth levels in America," while 60 percent said it's "more important to ensure everyone in America has the opportunity to reach the highest echelon of income and wealth even if not everyone makes it."

But in the context of the 2016 election, it's worth exploring.

Republicans, too, have been working on getting a bite at the populist pie. Sens. Ted Cruz (R-Tex.) and Marco Rubio (R-Fla.) have used their announcements to emphasize their humble roots, while Sen. Rand Paul (R-Ky.) and former Florida governor Jeb Bush (R) have talked about the GOP reaching out to the poor.

But for the GOP, talking about income inequality is still a tough nut to crack. A party built on the free market, small government and equality of opportunity, after all, has long decried the concept of redistribution of wealth. And talking about fixing income inequality is a slippery slope toward the "R"-word or even the "S"-word (socialism).

So what does this poll say about the GOP's task?

First of all, let's emphasize that it's not too surprising that people choose upward mobility over income inequality. After all, helping "middle and working class" Americans get ahead makes inequality less of an issue in and of itself. It's like killing two birds with one stone. And Clinton's "deck is stacked" message, to our mind, could be seen as catering to both people who choose Option No. 1 and Option No. 2.

But even if the poll question is something of an imperfect or false choice, it does hint at the limits of the income inequality argument. If Republicans can effectively tailor their economic message more toward Option No. 2 -- lifting up the middle and working class -- it could certainly mitigate whatever advantage Democrats have on the income inequality front.

Of course, aspiring to that kind of message and employing it effectively are two different things. And for now, Clinton has a clearer economic focus while the GOP is still searching for its path forward as it attempts to woo lower-income voters.

But if nothing else, this poll suggests the "deck is stacked" message has its limits -- or at least, more so than that 83 percent figure suggests.