As Hillary Clinton begins her presidential campaign, one fundamental question will determine the outcome of the 2016 presidential election: Is the coalition of voters that President Obama put together in his 2008 and 2012 victories indicative of a permanent change in the American electorate that favors any Democratic candidate? Or were the super-sized margins Obama enjoyed among groups such as minorities and young voters specific to the first African-American president?

If demographics are destiny, then Republicans will be in danger no matter how strong a campaign they mount against Clinton. If not — and if she can't make up votes with other groups of voters — her candidacy will likely fail.

The challenge of keeping Obama's coalition together is clearly on the minds of Clinton's campaign strategists. The carefully orchestrated video announcing her candidacy released on Sunday featured a cross-section of Americans from diverse racial backgrounds as well as gay and lesbian couples. The transparent purpose was to exploit the image of Republicans as being out of touch with the changing nature of the American electorate.

A look at exit polls dating back to 1976 from the Roper Center (and CNN) shows that Obama is in a league of his own when it comes to Democratic victory margins among young voters and African-Americans.

Obama's candidacy represented a historic opportunity for black voters that would no longer be present with Clinton, whom he bested in the 2008 Democratic nomination contest. No doubt, Democrats have traditionally dominated among black voters in recent history. Between the time of Jimmy Carter's victory over Gerald Ford and John Kerry's loss to George W. Bush in 2004, Democrats won black voters by an average of nearly 75 points. But Obama won the group by 91 points in 2008 and 87 points in 2012.

Also, in Obama's victories, black voters comprised 13 percent of the electorate — even though, in the prior eight presidential elections, African-Americans never made up more than 11 percent of the electorate and comprised as little as 8 percent (that was in 1992, when Bill Clinton won his first term in the White House).

These might seem like marginal changes, but they could well be determinative. If Hillary's performance among black voters retreats to more typical Democratic levels, it will hinder her efforts in swing states such as Ohio and Florida, where Democrats need to rack up huge margins in urban areas to make up for their weaknesses in other parts of the states.

When it comes to the youth vote, Obama's commanding performance relative to his Democratic predecessors is even more apparent. Between 1992 and 2004, Democrats won the 18 to 24 vote by an average 11.5 point margin and the 25 to 29 vote by an even narrower margin of just over 7 points. But Obama won the same age groups by over 30 points in 2008, and over 20 points in 2012. Even in 2012, Obama's performance was stronger than Bill Clinton's 1996 re-election campaign in which he was running on a strong economy against a septuagenarian Bob Dole (though that year's data could be skewed due to the presence of third party candidate Ross Perot).

In 2008, Obama was a fresh-faced, 47 year-old Senator who was new to the political scene and offered a message of change — vowing to overcome cynicism with hope. In contrast, Hillary will almost certainly be older than the Republican nominee. It's questionable that young voters will flock to vote at historically high levels for a 69-year old white woman who has been a national political figure since before many of them were born.

Her efforts to woo younger voters could also open her up to charges of cynicism. Though her campaign launch video featured a gay couple holding hands, looking forward to their impending marriage, Clinton's record has been the subject of criticism from supporters of gay rights. She didn't come out in favor of gay marriage until 2013, when public opinion had already turned. As president, her husband Bill put in place the "Don't Ask, Don't Tell" policy toward gays in the military.

This doesn't even account for any potential erosion among the Hispanic vote should Republicans make inroads in that group — a major goal of the party, especially for candidates such as Marco Rubio and Jeb Bush.

If Hillary loses ground among these demographic groups, she'll have to make gains elsewhere. The campaign's most obvious targets are women (given that she'd be the first female president if elected) and working-class white voters (hence the emphasis in her announcement on being a champion of the middle class).

But even here, it isn't clear that she can improve substantially on Obama's performance. In both of his campaigns, Obama already did better among female voters than almost any other Democratic candidate since data are available in 1976. In 2004, Kerry only won women by 3 points, but Obama won them by 13 points in 2008 and 11 points in 2012. The one candidate who did better was Clinton in 1996, who won women by 17 points that year. However, once again, it's unclear how the Perot factor may have affected this margin.

As far as white voters, this is more debatable. According one school of thought, Obama's race hindered his performance among working-class whites. Though it's true that in his re-election campaign, Obama lost the white vote by 20 points, the racial thesis is undercut by the fact that in his first campaign, the margin was a narrower 12 points. His performance among whites in 2008 was actually better than white Democratic nominees Al Gore and Kerry in the previous two election cycles.

It could be seen as encouraging that Hillary's husband Bill narrowly lost the white vote during his campaigns — by just two points each time. But the Perot factor is especially strong among this demographic, as he took a large share of the white vote.

Additionally, the shift of the working-class white vote away from Democrats is more likely explained by a broader trend rooted in Democratic policy priorities, rather than a function of Obama. Environmental policies that may be popular on the coasts and on college campuses, for instance, are less popular among working-class voters in states with large or growing energy sectors. As an example, West Virginia, one of only 10 states carried by 1988 Democratic nominee Michael Dukakis, has become solidly Republican.

This isn't to suggest that Clinton won't be able to cobble together a sufficient coalition to win the presidency. But those Democrats who dismiss her vulnerabilities as a candidate on the assumption that the Obama electorate will turn out for her could be in for a rude awakening in November 2016.