DES MOINES, Iowa (AP) -- The leading Democrats vying for their party's presidential nomination clashed over the critical issue of health care while offering starkly contrasting visions for the nation's ideological direction before thousands of cheering Iowa activists at a raucous event kicking off the three-month sprint to the first-in-the-nation caucuses.
Former Vice President Joe Biden opened the state Democratic Party's marquee annual fundraiser, the Liberty and Justice Celebration, by swiping at the candidate who has largely caught him atop the Democratic primary polls, Massachusetts Sen. Elizabeth Warren. Meanwhile, Pete Buttigieg, the 37-year-old mayor of South Bend, Indiana, pledged generational change, trying to take up the mantle of another young, upstart candidate, Barack Obama, who pulled off a 2008 upset in Iowa on his way to the presidency.
The jabs were relatively gentle but previewed arguments that are likely to increasingly dominate the race.
Biden said he would overhaul health care nationwide without "increases in taxes for the middle class. None. None. None." While not mentioning Warren by name, his pronouncement came hours after she unveiled a much-anticipated proposal to spend $20-plus trillion over the next decade on a "Medicare for All" universal health care plan that she vowed wouldn't require a middle-class tax increase. Biden's campaign had already panned that as requiring "mathematic gymnastics" to cover its huge costs.
The former vice president has promised not to "abandon" Obama's signature health care law. The issue has created a stark policy divide between Warren and Vermont Sen. Bernie Sanders, both of whom back Medicare for All, and more moderate candidates like Biden and Buttigieg, who say the country isn't ready to do away with private insurance.
Biden also called for party unity and tried to cast himself as immediately able to rise to international challenges: "The next president is going to be commander in chief of a world in disarray. There's going to be no time for on-the-job training."
Taking the stage a short time later, Warren made an unwavering appeal for sweeping change, saying, "If the most we can promise is business as usual after Donald Trump, then we will lose."
"It's easy to give up on a big idea, but when we give up on a big idea, we give up on the people whose lives would be touched by that big idea," she said. "Anyone who comes on this stage and tells you to dream small and give up early is not going to lead our party to victory."
In all, more than a dozen presidential candidates addressed 13,000-plus Democratic activists, party volunteers and campaign supporters at a basketball arena in downtown Des Moines. The event amounts to the largest gathering of Democrats in an early voting state — and was something of a dress rehearsal for the Feb. 3 caucuses. Candidates must now move beyond simply introducing themselves to voters and activists and focus on perfecting a grassroots strategy to ensure they mobilize strong support.
For White House hopefuls in the top tier, the event was a key test of momentum, while lagging contenders will face further questions about why they're staying in the race. That was on full display even before Friday's festivities began, with former Texas Rep. Beto O'Rourke abruptly announcing he was abandoning his campaign.
Like Biden, Buttigieg didn't mention Warren by name but said he supported "Medicare for all who want it" and promised to honor the decisions of those who aren't willing to sign up for fully government-sponsored health care. The 37-year-old also offered a veiled swipe at Warren, Biden and Sanders — all in their 70s — by chiding candidates for being content to "wait for action."
"I am running to be the president who will stand amid the rubble, pick up the pieces of our divided nation and lead us to real action to do right by Americans who have waited far too long," Buttigieg said.
A New York Times/Siena College poll of likely caucusgoers released Friday found Warren, Sanders, Buttigieg and Biden bunched together at the top of the field in Iowa, though Biden and Warren have generally been co-front-runners elsewhere.
Sanders struck his familiar, defiant tone Friday night, telling the crowd, "We will pass, whether the insurance companies like it or not, Medicare for All."
The event really started hours before the formal program. The damp, chilly streets outside the arena buzzed all afternoon with campaigns hoping to exhibit strong organization and enthusiasm. Supporters and campaign volunteers waved signs at busy street corners and congregated in chanting droves.
Sanders led a pre-event march that his campaign said drew 1,500 people. Warren supporters erected a giant likeness of Bailey, the senator's golden retriever. Inside the arena, Biden bought tickets for members of the International Association of Fire Fighters, which has endorsed him, while Buttigieg had the largest presence, snapping up thousands of seats for supporters that included an overflow room.
Candidates who have traditionally wowed at the gathering have seen it pay big dividends. In 1999, then-Vice President Al Gore effectively blocked former New Jersey Sen. Bill Bradley's advance with the chant during his speech "Stay and fight," a nudge at Bradley for leaving the Senate.
Four years later, Massachusetts Sen. John Kerry used it to hold off a dire challenge from Howard Dean.
"We need answers, not just anger," Kerry said in a hit at the anti-war Vermont governor who had stirred passions on the left but worried others for challenging President George W. Bush during wartime. "Iowa, don't just send them a message. Send them a president."
More recently, Obama, then an Illinois senator, threw down the gauntlet against national Democratic front-runner Hillary Clinton in 2007, declaring, "Triangulating and poll-driven positions, because we're worried about what Mitt or Rudy might say about us, just won't do."