Democratic presidental candidate Hillary Clinton says there is a lot she would do "to build on the successes of President Obama," but says her proposed plans go beyond his current politics. (CNN)

Front-runner Hillary Rodham Clinton dominated the debate stage Tuesday night.

Her experience and self-assurance in a setting where she has found herself dozens of times put her in command as she and her four lesser-known rivals for the Democratic nomination stood side by side for the first time.

In several exchanges, she managed to put her leading challenger, the combative Sen. Bernie Sanders (I-Vt.), in an unaccustomed position — on defense.

At the same time, Clinton and Sanders offered their party a choice. She presented herself as realist who would work from within to improve the political system; he, as an unapologetic insurgent who would smash the old order.

Clinton appeared to be ­positioning herself for a general-election campaign against whichever Republican emerges from that party’s nomination brawl.

“I’m a progressive. But I’m a progressive who likes to get things done. And I know how to find common ground, and I know how to stand my ground,” said the former secretary of state, senator and first lady.

Sanders brought to the debate the same umbrage that has been drawing liberal crowds that number in the tens of thousands at his rallies across the country

He bristled as he spoke of what he said is “a series of unprecedented crises. The middle class of this country for the last 40 years has been disappearing.”

“What this campaign is about is whether we can mobilize our people to take back our government from a handful of billionaires and create the vibrant democracy we know we can and should have,” added the Vermont senator, who describes himself as a democratic socialist.

The contrast between Clinton and Sanders crystallized early in the debate over a single word: capitalism.

Asked whether he supports the driving force of the American economic system, Sanders said, “Do I consider myself part of the casino capitalist process by which so few have so much and so many have so little, by which Wall Street’s greed and recklessness wrecked this economy? No, I don’t. I believe in a society where all people do well. Not just a handful of billionaires.”

To which Clinton rejoined, “When I think about capitalism, I think about all the small businesses that were started because we have the opportunity and the freedom in our country for people to do that and to make a good living for themselves and their families.”

Candidates including Hillary Clinton and Bernie Sanders took on gun control, Benghazi and other big issues at the first Democratic presidential debate of the 2016 race. Here are the highlights. (Sarah Parnass/The Washington Post)

Clinton began the race as the most formidable non-incumbent front-runner in memory. She was thought to have learned from the mistakes of her first presidential campaign, in 2008. Her dominance was such that virtually the entire Democratic establishment was lining up behind her, and she appeared to have effectively cleared the field.

But the controversy over her use of a private e-mail account and server, rather than a government account and server, while she was secretary of state has deepened public misgivings about her character and honesty.

Meanwhile, Sanders has capitalized on the deep populist discontent within the Democratic base.

One of their sharpest exchanges came on the question of how much government muscle should be applied to reining in Wall Street.

Sanders, along with former Maryland governor Martin O’Malley, blamed the deregulation that took place during Bill Clinton’s presidency for creating the conditions that sparked the financial collapse of 2008. Specifically, they cited Bill Clinton’s role in the repeal of the Glass-Steagall Act, a Depression-era banking regulation that limited banks’ financial activities.

“Let us be clear that the greed and recklessness and illegal behavior of Wall Street, where fraud is a business model, helped to destroy this economy and the lives of millions of people,” Sanders said.

Hillary Clinton, who many liberals believe has been too close to Wall Street, said that she had used her influence as a senator from New York to press the banks to quit engaging in irresponsible financial speculation.

“But I’m telling you — I will say it tonight. If only you look at the big banks, you may be missing the forest for the trees,” Clinton said.

The other candidates also revisited the question that had dogged Clinton in her earlier bid for the Democratic nomination: her vote in support of the 2003 invasion of Iraq.

Clinton, who has since said she regretted that decision, cited the man who beat her as validation that it was not a disqualifier.

”I recall very well being on a debate stage, I think, about 25 times with then-Senator Obama, debating this very issue. After the election, he asked me to become secretary of state,” she said. “He valued my judgment, and I spent a lot of time with him in the Situation Room, going over some very difficult issues.”

Clinton maintains a double-digit lead in the national polls, but Sanders is trailing her narrowly in Iowa, where the first caucuses are to be held Feb. 1, and is leading her in New Hampshire, which is set to hold its primary eight days later.

The debate was the first in a series of October events that Clinton hopes will change the trajectory of her struggling presidential campaign. Next week, she will testify before the House Select Committee on Benghazi, whose investigation she and her allies say is politically motivated and aimed at destroying her candidacy.

She did it again during the debate, pointing to a recent comment by House Majority Leader Kevin McCarthy (R-Calif.).

“This committee is basically an arm of the Republican National Committee,” she said. “It is a partisan vehicle, as admitted by the House Republican majority leader, Mr. McCarthy, to drive down my poll numbers. Big surprise. And that’s what they have attempted to do.”

Three days after her congressional testimony, she and the other Democratic contenders are to make high-profile speeches at an annual Democratic dinner in Iowa that has often been an important moment in the primary season.

The coming days are also likely to bring the resolution of a question that has been hanging over the 2016 Democratic race: Will Vice President Biden jump in?

Clinton’s performance Tuesday night showed that she remains the person to beat.