Now that the 2014 elections are over and national politics is all about 2016, Democrats have good reason to worry that, for all his success at the polls, President Obama will leave his party with a toxic legacy.

The Obama damage is two-fold. First, his success relied on a coalition that likely will not survive, or at least survive at full strength, without Obama himself on the ticket. Secondly, Obama drove a significant portion of white voters away from the Democratic Party.

Put those two things together — smaller Obama coalition and more alienated whites — and the result could be huge trouble for whoever the Democratic presidential nominee is in 2016.

First the coalition: Obama's powerful appeal to minorities, women, and young people propelled his decisive wins in 2008 and 2012. But those voters didn't show up at the polls in 2010 and 2014.

Some Democrats are confident the coalition will be back in 2016, when interest in a presidential race is far greater than during midterms. But will it return in the strength it showed in '08 and '12? Or will Democratic voting return to pre-Obama patterns?

On the question of minorities, in 2004, the last presidential election in which Obama was not on the ballot, the Democratic nominee, John Kerry, won 88 percent of the black vote, 53 percent of the Hispanic vote, and 56 percent of the Asian vote, according to exit polls.

Four years later, Obama won 95 percent of the black vote, 67 percent of the Hispanic vote, and 62 percent of the Asian vote. And those were higher percentages of higher turnout than in 2004, as well. Obama racked up big wins with those groups again in 2012.

It would be risky for Democrats to assume those voters will turn out at the same rate and vote in the same proportions for a Democratic candidate in 2016. Yes, it's a lock that the Democrat will win the minority vote, but by the same margins?

As far as women are concerned, Kerry won 51 percent in 2004, while Obama won 56 percent in 2008. If Hillary Clinton is the Democratic nominee, could she top Obama's performance with women, given the party's other problems? That's another risky Democratic bet.

Kerry won 54 percent of voters age 18 to 29. Four years later, Obama won 66 percent. The president's showing among those voters fell to 60 percent in 2012, but it's not hard to imagine the next Democratic candidate falling short of even that performance.

Then there are white voters. Obama's overall job approval rating among whites is a weak 32 percent, according to Gallup. Two-thirds of whites do not have a college degree, and the president's approval rating among them is 27 percent.

The Democrats' problem with those voters is perhaps symbolized by Obama but goes far beyond the president himself. "Given its sheer size, the working-class white population in the U.S. is of keen importance to politicians and strategists on both sides of the aisle," Gallup wrote recently, noting "the complex set of attitudes and life positions which … have pushed this group further from the Democratic president over the past six years."

If Democrats don't find a way to connect with those "attitudes and life positions" of working-class whites in coming years, they'll have a big problem.

In a recent speech, Sen. Charles Schumer, D-N.Y., argued that his party made its middle-class problem worse by insisting on passing Obamacare, which imposed burdens on millions and focused its most generous benefits on a relatively small group of Americans at a time when most voters wanted their elected leaders to focus on jobs and the economy.

"To aim a huge change in mandate at such a small percentage of the electorate made no political sense," Schumer said in a November 24 speech at the National Press Club. "So when Democrats focused on health care, the average middle class person thought, 'the Democrats are not paying enough attention to me.'"

Some Democrats are hoping demographic change will push them to victory in 2016. Yes, there will be more Hispanic voters in '16 than in '12. But persuading them to support the Democratic candidate in the same numbers they did Obama won't be easy.

In the end, no single group will mean defeat for the Democrat and victory for the Republican in 2016. But President Obama's troubling legacy — a weakened coalition and growing ranks of alienated white voters — could mean a serious post-presidential hangover for Democrats.