Hillary Rodham Clinton has locked up public support from half of the Democratic insiders who cast ballots at the party's national convention, giving her a commanding advantage over her rivals for the party's presidential nomination.

Clinton's margin over Vermont Sen. Bernie Sanders and former Maryland Gov. Martin O'Malley is striking. Not only is it big, but it comes more than two months before primary voters head to the polls -- an early point in the race for so many of the people known as superdelegates to publicly back a candidate.

"She has the experience necessary not only to lead this country, she has experience politically that I think will help her through a tough campaign," said Unzell Kelley, a county commissioner from Alabama.

"I think she's learned from her previous campaign," he said. "She's learned what to do, what to say, what not to say -- which just adds to her electability."

The Associated Press contacted all 712 superdelegates in the past two weeks, and heard back from more than 80 percent. They were asked which candidate they plan to support at the convention next summer.

The results:

Clinton: 359.

Sanders: 8.

O'Malley: 2.

Uncommitted: 210.

The 712 superdelegates make up about 30 percent of the 2,382 delegates needed to clinch the Democratic nomination. That means that more than two months before voting starts, Clinton already has 15 percent of the delegates she needs.

That sizable lead reflects Clinton's advantage among the Democratic Party establishment, an edge that has helped the 2016 front-runner build a massive campaign organization, hire top staff and win coveted local endorsements.

Superdelegates are convention delegates who can support the candidate of their choice, regardless of who voters choose in the primaries and caucuses. They are members of Congress and other elected officials, party leaders and members of the Democratic National Committee.

Clinton is leading most preference polls in the race for the Democratic nomination, most by a wide margin. Sanders has made some inroads in New Hampshire, which holds the first presidential primary, and continues to attract huge crowds with his populist message about income inequality.

But Sanders has only recently started saying he's a Democrat after a decades-long career in politics as an independent. While he's met with and usually voted with Democrats in the Senate, he calls himself a democratic socialist.

"We recognize Secretary Clinton has enormous support based on many years working with and on behalf of many party leaders in the Democratic Party," said Tad Devine, a senior adviser to the Sanders campaign. "But Sen. Sanders will prove to be the strongest candidate, with his ability to coalesce and bring young people to the polls the way that Barack Obama did."

"The best way to win support from superdelegates is to win support from voters," added Devine, a longtime expert on the Democrats' nominating process.

The Clinton campaign has been working for months to secure endorsements from superdelegates, part of a strategy to avoid repeating the mistakes that cost her the Democratic nomination eight years ago.

In 2008, Clinton hinged her campaign on an early knockout blow on Super Tuesday, while Obama's staff had devised a strategy to accumulate delegates well into the spring.

This time around, Clinton has hired Obama's top delegate strategist from 2008, a lawyer named Jeff Berman, an expert on the party's arcane rules for nominating a candidate for president.

Clinton's increased focus on winning delegates has paid off, putting her way ahead of where she was at this time eight years ago. In December 2007, Clinton had public endorsements from 169 superdelegates, according to an AP survey. At the time, Obama had 63 and a handful of other candidates had commitments as well from the smaller fraction of superdelegates willing to commit to a candidate.

"Our campaign is working hard to earn the support of every caucus goer, primary voter and grassroots and grasstop leaders," said Clinton campaign spokesman Jesse Ferguson. "Since day one we have not taken this nomination for granted and that will not change."

Some superdelegates supporting Clinton said they don't think Sanders is electable, especially because of his embrace of socialism. But few openly criticized Sanders and a handful endorsed him.

"I've heard him talk about many subjects and I can't say there is anything I disagree with," said Chad Nodland, a DNC member from North Dakota who is backing Sanders.

However, Nodland added, if Clinton is the party's nominee, "I will knock on doors for her. There are just more issues I agree with Bernie."

Some superdelegates said they were unwilling to publicly commit to candidates before voters have a say, out of concern that they will be seen as undemocratic. A few said they have concerns about Clinton, who has been dogged about her use of a private email account and server while serving as secretary of state.

"If it boils down to anything I'm not sure about the trust factor," said Danica Oparnica, a DNC member from Arizona. "She has been known to tell some outright lies and I can't tolerate that."

Still others said they were won over by Clinton's 11 hours of testimony before a GOP-led committee investigating the attack on a U.S. consulate in Benghazi, Libya. Clinton's testimony won widespread praise as House Republicans struggled to trip her up.

"I don't think that there's any candidate right now, Democrat or Republican, that could actually face up to that and come out with people shaking their heads and saying, `That is one bright, intelligent person,"' said California Democratic Rep. Tony Cardenas.