A once-sleepy Democratic presidential primary contest is fast coming alive as Hillary Rodham Clinton’s poll numbers fall and a diverse array of long-shot opponents step forward to challenge her.

The recent developments mark a dramatic evolution in the 2016 sweepstakes, which until now has been shaped by the large assortment of hopefuls on the Republican side, where there is no front-runner.

The latest Democrat to enter the race is Lincoln Chafee, a onetime Republican and former Rhode Island governor and senator, who launched his campaign Wednesday in Northern Virginia. Though his candidacy is quixotic, Chafee’s sharp attacks on Clinton’s hawkish foreign policy record — and in particular her 2002 vote to authorize the war in Iraq — could nonetheless complicate her march to the nomination.

Chafee joins an underfunded and jumbled field of Clinton rivals who see the favorite’s coziness with Wall Street and political longevity as weaknesses and who think she is vulnerable to a grass-roots contender who better captures the party’s liberal soul.

Sen. Bernie Sanders (I-Vt.), a fiery populist who identifies as a socialist, has been attracting some of the largest crowds of any candidate from either party as he summons supporters to join his "political revolution."

Former U.S. senator and Rhode Island governor Lincoln Chafee announces he is running in the 2016 presidential race. (Video: AP)

Another foe, former Maryland governor Martin O'Malley, is making an overt generational contrast: His campaign slogan is "New Leadership." And former senator Jim Webb of Virginia has echoed Chafee's antiwar pitch as he explores a candidacy.

The activity has brought fresh attention to the fault lines within the Democratic coalition over economic fairness and foreign policy.

At Clinton’s Brooklyn headquarters, the mantra has been to prepare for a difficult primary and compete for every vote in every state. Her team has carefully crafted a summer rollout — a June 13 kickoff rally followed by major policy speeches — to cast Clinton as a progressive champion.

On Thursday, for instance, Clinton will give a speech on voting rights at a historically black college in Texas, where she will call for an early voting period of at least 20 days in every state. Her address comes as Democrats pursue legal challenges to voting restrictions ushered in by Republican legislatures.

“We’ve always thought there would be challengers,” Clinton campaign chairman John D. ­Podesta said in an interview Wednesday. “There were always going to be people saying she wasn’t this enough, wasn’t that enough, wasn’t populist enough.”

He added: "Our strategy at the moment is to welcome them into the race and lay out our program versus theirs. . . . There will be debates. These candidates will get their airtime. But what we're focused on is telling her story, what her vision for the country is."

Running left, Hillary Clinton is banking on the Obama coalition to win

Polls show that Clinton’s popularity is foundering with her reemergence as a political candidate, effectively erasing the bipartisan approval she enjoyed as secretary of state.

More Americans said they held an unfavorable opinion of Clinton than a favorable one, 49 percent to 45 percent, according to a Washington Post-ABC News poll this week. Among independents, the figure is worse: 55 percent unfavorable to 39 percent favorable.

Republicans are pleased to see Clinton’s popularity coming down to earth.

“Clearly, whatever political capital that Hillary Clinton had previously enjoyed as secretary of state has atrophied,” said pollster Neil Newhouse, who is likely to work for Right to Rise, the pro-Jeb Bush super PAC.

Still, Clinton is trouncing the rest of the Democratic field by every measure, including in money raised and in the depth of her organization. Her campaign has opened nine field offices in Iowa, which hosts the first presidential caucuses.

This week’s Post-ABC poll showed Clinton leading the Democratic pack at 62 percent. Vice President Biden, who has not formally ruled out a candidacy, was second with 14 percent, followed by Sanders at 10 percent.

Paul Begala, an adviser to the pro-Clinton super PAC Priorities USA Action, predicted that the race will tighten.

“The day she announced, the polls had her at like a million percent,” Begala said. “She needed to print that out, put it in a scrapbook and give it to baby Charlotte, because it will never be this good again.”

Clinton is showing political fragility in some areas, including on character attributes. Fifty-two percent of those polled said she was not honest and trustworthy.

An unlikely contender: Bernie Sanders takes on ‘billionaire class’

Clinton’s advisers attribute this to intense media scrutiny. They argue that a more accurate barometer of her standing is the question of empathy. Asked whether she “understands the problems of people like you,” 49 percent said she did and 46 percent said she did not.

Anastasia Rave, 26, a retail manager in Beaufort, N.C., was among those polled. A Democratic-leaning independent, Rave said she would support Clinton over any Republican candidate — but she remains uneasy.

“I don’t think that her attempts to act like she understands the everyday working person are genuine,” Rave said. “I don’t really buy it.”

The Clinton response is to give speeches on issues such as college affordability in an effort to show her as compassionate toward the middle class.

“The real trust issue in the election will be who voters trust to look out for them,” said pollster Geoff Garin of Priorities USA.

To Democrats who are fretting, Ed Rendell, a former Pennsylvania governor and a Clinton booster, has a blunt message: “Man up.”

“No matter who the candidate was — if Moses or Jesus or Muhammad came back — there would be time periods when they were considered untrustworthy by the public,” Rendell said. “If you’re not convinced that Hillary’s a lights-out candidate, tell me who is?”

A swelling number of liberal activists, however, see Sanders as the answer. The boisterous crowds that have greeted his road show in the two weeks since he launched his campaign have surprised even his longtime advisers.

With his Brooklyn-accented barbs about what he believes is the alarming power of corporate America, Sanders sees a path to defeating Clinton. While Clinton is flanked by aides and Secret Service agents at controlled events, Sanders revels in rowdy town hall meetings and wanders through crowds wearing a rumpled suit and with unruly white hair.

“I don’t want to get too socialist about it, but I’d describe it as communal,” said Sanders political consultant Tad Devine.

Sanders has instructed his inner circle to concentrate on the economy rather than Clinton’s Iraq vote, even though that is one front where their records differ. “We don’t want a campaign about something that happened 12 or 13 years ago,” Devine said. “It’s got to be about the next 10.”

But Iraq is a centerpiece of Chafee’s appeal to Democrats.

“It’s heartbreaking that more of my colleagues failed to do their homework,” Chafee said Wednesday as he announced his candidacy at George Mason University. “And incredibly, the neocon proponents of the war who sold us on the false premise of weapons of mass destruction are still key advisers to a number of presidential candidates today.”

He added later: “Including the main Democratic candidate.”

Lincoln Chafee on the Iraq war: ‘I did not make that mistake’

Chafee’s approach is reminiscent of how then-Sen. Barack Obama used Clinton’s Iraq vote to drive a wedge between her and antiwar Democrats in 2008. Clinton has since disavowed the vote, and some supporters believe the war is no longer a central concern for voters.

“When I ran [in 2004], it was a different party and frightened about the war,” said former Vermont governor Howard Dean, a Clinton backer.

O’Malley, 52, is offering himself as a youthful alternative to Clinton palatable to all wings of the party, while also railing against “the privileged and the powerful” as he said this past weekend.

O’Malley and his associates are targeting those who tried unsuccessfully to draft Sen. Elizabeth Warren (D-Mass.) to run. A super PAC supporting O’Malley said Wednesday that it will soon purchase a round of television ads in Iowa highlighting his willingness to battle Wall Street, though a spokesman said the initial buy is a modest $25,000.

“There is a real hunger for economic populism. O’Malley is speaking to that,” said George Appleby, O’Malley’s state chairman in Iowa. He called Sanders “honorable and interesting” but said that “I’d be very surprised if Democrats nominated a 73-year-old man.”

John Wagner, Jose DelReal and Peyton Craighill contributed to this report.