One number shows why Joe Biden may be a stronger alternative than Bernie Sanders

Vice President Joe Biden is reportedly close to announcing his decision on a third presidential run.

And if he does, he'll have at least one advantage over Sen. Bernie Sanders (I-Vermont) as a potential alternative to front-runner Hillary Clinton.

A new Monmouth University poll released Monday reflects what's been more or less the general shape of the race for the last several months. Clinton remains the clear front-runner: Monday's poll showed Clinton with 48% support among Democratic voters nationally, compared to Sanders' 21% and Biden's 17%.

But the poll also displayed a result that may be key to Biden's campaign, should he decide to run.

The vice president appeals to a vast and more diverse pool of primary voters than Sanders. Biden has a 71% favorability rating among white Democratic voters, as well as a 72% favorable rating among black and Hispanic Democrats.

Sanders support is much narrower and relies heavily on white voters. According to the latest poll from Monmouth, 70% of white Democratic voters held a favorable view of the senator, while only 42% of black and Hispanic Democrats said they viewed Sanders in a positive light.

The numbers reflect trends found in other polls of key primary states. A CNN/ORC poll of South Carolina released last week found Sanders with only 7% support among black voters there, an enormous deficit in a state where the majority of the electorate is non-white.

Sanders' popularity among white voters will certainly help him in states like Iowa and New Hampshire, where the electorate is overwhelmingly white and somewhat mirrors the support that Sanders has built in his home state of Vermont. Indeed, he has the strongest levels of support in the Hawkeye and Granite States.

But he may struggle in states like South Carolina, the third-nominating state. Clinton is currently the overwhelming front-runner there, and Biden has strong ties to the state.

For his part, Sanders has acknowledged his deficits among minority voters, and he has said he will do more to win support in minority communities.

"I'm not well known in the African-American community, despite a lifelong record," Sanders told The New York Times earlier this year. "That's a real issue, and I have to deal with it."

Biden trails Sanders in the Democratic horserace, but polls like Monmouth's survey show that he has more room to grow. According to the poll, 73% of likely Democratic voters said they hold a favorable view of the vice president. That's higher than the 60% who favor Sanders, whose favorable numbers have risen in the last several weeks.

But polls have also discovered significant challenges for Biden: namely, that he'd be most directly competing with Clinton for votes.

A recent Public Policy Polling poll found Biden to be the top second choice candidate among Democrats, with 26% reporting the vice president was their second choice. Biden's performance in states like South Carolina would rely on him siphoning votes from Clinton, which according to many recent polls is not happening at this stage in the race.