As Hillary Clinton starts her second run for the presidency, one statistic stands out: 47 percent.

Mitt Romney made that number notorious by saying that 47 percent of Americans "are dependent on government (and) believe that they are victims," and so will automatically vote Democratic.

That quote helped sink Romney as a clueless rich guy, but Clinton has a different "47 percent" problem. That's the number, according to the latest ABC/Washington Post poll, who think Hillary "understands the problems of people like you." Forty-eight percent say she doesn't get it.

That question might sound vague, but political pros know how important it is. It tries to measure a critical set of qualities that include compassion and connectedness, sincerity and sensitivity.

If Clinton cannot convince more voters that she possesses those virtues, she will have a hard time winning the White House next year.

History reinforces this point. Even when Barack Obama's re-election campaign was staggering under the burden of a stagnant economy and a 7.5 percent unemployment rate, the president always led Romney by double digits on the empathy index.

On Election Day, 21 percent told exit polls that their top concern was backing a candidate "who cares about people like me." Of those voters, 4 out of 5 supported Obama.

As longtime ABC pollster Gary Langer explains: "The sense that elected leaders understand the problems of average Americans can be an indispensable asset in election politics -- it went a long way, for example, in lifting Barack Obama over Mitt Romney."

Of course, issues matter, and there will be plenty of time for Clinton to detail her views on war in the Middle East and wages in the Midwest. But after covering politics for more than 50 years, we believe strongly that Langer is right: Personality often trumps policy.

Choosing a president is a gut check for most voters. They know on some level that many of the issues facing the next president cannot be predicted with any certainty. The fight against terrorism was barely discussed during the 2000 campaign, for example, and yet after 9/11, the Bush presidency was consumed by that battle.

That's why voters so often focus on a candidate's character. They want someone they can count on to protect their interests as new challenges emerge.

"Will voters find her honest, authentic and empathetic enough to entrust her with their futures?" Dan Balz wrote of Hillary in The Washington Post. "Where Clinton's candidacy is likely to rise or fall is on how the American people respond to her personally."

This issue of personal appeal is often summed up in the question: "Who would you rather have a beer with?" Likability is always a valuable trait in any politician, and Clinton has never scored well on the Warmth Meter.

But the beer trope trivializes what's really at stake. A better question is, "Who do you believe in?" Or put another way, "Who believes in you?"

Team Hillary clearly understands this. That's why a memo written by campaign manager Robby Mook described her focus as "the everyday Americans who are trying to build a better life for themselves and their families."

In the same vein, her introductory video starred those "everyday Americans," not the Washington insiders or world leaders she knows so well. And then she drove to Iowa in a van, stopping for lunch at a Chipotle in Maumee, Ohio -- where no one recognized her.

Connecting to those "everyday Americans" will not be easy. Even friendly critics have derided her campaign debut as contrived and phony. Post columnist Ruth Marcus called her video "relentlessly, insultingly vapid," and comedian Jon Stewart compared it to a "State Farm commercial gone viral."

Langer describes another impediment: "Clinton may have a particular dilemma, one based on ingrained gender stereotypes: Experimental research shows that when women are perceived as competent and powerful, they are less apt to be seen as warm and friendly, compared with identically described men."

Clinton starts with enormous strengths. She's one of the most experienced candidates ever to seek the presidency, and the possibility of becoming the first female chief executive injects her campaign with an invaluable dose of energy and excitement.

Elections are always choices between two candidates, not votes of confidence, and Clinton beats every Republican hopeful by double digits in national polls (although swing state surveys are closer).

But come November of next year, if only 47 percent of the voters think Clinton understands them, she'll be in trouble.