The battle for Iowa took center stage at the Democratic debate in Los Angeles on Thursday night as top-tier candidates collided and the long shots made their moves with only 46 days until the first-in-the-nation caucuses.

Polls are pointing toward a photo finish in Iowa and momentum will matter, as South Bend, Ind., Mayor Pete Buttigieg Pete ButtigiegBillionaire who donated to Trump in 2016 donates to Biden The Hill's Morning Report - Sponsored by Facebook - GOP closes ranks to fill SCOTUS vacancy by November Buttigieg stands in as Pence for Harris's debate practice MORE looks to maintain his narrow lead over Sen. Bernie Sanders Bernie SandersTrump, Biden will not shake hands at first debate due to COVID-19 Sanders tells Maher 'there will be a number of plans' to remove Trump if he loses Sirota reacts to report of harassment, doxing by Harris supporters MORE (I-Vt.), Sen. Elizabeth Warren Elizabeth WarrenOvernight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds On The Money: Half of states deplete funds for Trump's 0 unemployment expansion | EU appealing ruling in Apple tax case | House Democrats include more aid for airlines in coronavirus package Warren, Khanna request IG investigation into Pentagon's use of coronavirus funds MORE (D-Mass.) and former Vice President Joe Biden Joe BidenBiden says voters should choose who nominates Supreme Court justice Trump, Biden will not shake hands at first debate due to COVID-19 Joe Biden should enact critical government reforms if he wins MORE.

And it’s now or never for candidates such as Sen. Amy Klobuchar Amy Klobuchar3 reasons why Biden is misreading the politics of court packing Social media platforms put muscle into National Voter Registration Day Battle lines drawn on precedent in Supreme Court fight MORE (D-Minn.) and tech entrepreneur Andrew Yang Andrew YangBiden's latest small business outreach is just ... awful Doctor who allegedly assaulted Evelyn Yang arrested on federal charges The Hill's Campaign Report: Biden weighs in on police shootings | Who's moderating the debates | Trump trails in post-convention polls MORE.

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The knives were out against Buttigieg, whose surge to the top of the field in Iowa made him a prime target for his rivals.

Long-simmering tensions between the Buttigieg and Warren, who led the polls in Iowa only weeks ago, boiled over on the national stage, as the candidates clashed over free college tuition, raising money from millionaires and a wealth tax.

And Klobuchar, who is languishing in the polls but is staying afloat on the strength of her sharp debate performances, launched cutting attacks against Buttigieg, knowing that she has to get around the upstart mayor in Iowa if she’s to stay in the race for the long haul.

Biden and Sanders both posted strong debate performances that will leave supporters watching the polls to see if they can separate themselves from the pack ahead of the caucuses. They also engaged in a heated clash over health care, which has been the most divisive issue in the Democratic primary contest by far.

But the centerpiece of Thursday night’s debate was the extended exchange between Buttigieg and Warren, who have been on a collision course for weeks and are in desperate need of a top finish in Iowa.

The left has fumed over Buttigieg’s rise and views him as a threat to their progressive agenda.

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Warren took up the cause by challenging the South Bend mayor on a “wine cave” fundraiser he held with wealthy donors beneath “crystal chandeliers” with “$900 bottles of wine.”

"Billionaires in wine caves should not pick the next president of the United States,” Warren said.

The attack had been telegraphed for weeks and Buttigieg knew it was coming. He responded with a shot at Warren’s own wealth, saying he is “literally the only person on this stage who is not a millionaire or a billionaire.”

"This is the problem with issuing purity tests you cannot yourself pass,” he said. “If I pledged to never be in the company of a progressive, Democratic donor, I couldn't be up here.”

That back and forth dragged on, provoking Klobuchar to interject.

"I've never even been to a wine cave. I've been to the wind cave in South Dakota, which I suggest you visit," she said.

Klobuchar’s entire campaign is riding on Iowa, so there may only be one more opportunity for her on the debate stage after Thursday.

She badly needs a top finish in the Hawkeye State, both as a senator with a connection to the Midwest and to build momentum ahead of New Hampshire.

The Minnesota senator had a strong debate, bringing a stable of memorable Midwest anecdotes and one-liners that she’s become known for.

Klobuchar went hard after Buttigieg, saying that at a previous debate he had “mocked” his rivals for their age and experience.

Klobuchar ticked through the accomplishments of the older candidates on stage, making the case that they had achieved far more than the 37-year-old mayor of South Bend.

“While you can dismiss committee hearings, I think this experience works,” Klobuchar said. “And I have not denigrated your experience as a local official, I have been one. I just think you should respect our experience when you look at how you evaluate someone who can get things done.”

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Buttigieg defended himself by bringing up his military experience and accusing Klobuchar of dismissing the importance of his small, Midwestern town.

“What happens in my city may seem small to you … but try putting together a coalition where 80 percent vote for you as a gay dude in Mike Pence Michael (Mike) Richard PenceFormer Pence aide: White House staffers discussed Trump refusing to leave office Pence vows for law and order everywhere Trump met with chants of protest as he pays respects to Ruth Bader Ginsburg MORE’s Indiana,” Buttigieg said.

The issue of health care once again ignited a fiery back and forth at the the debate, this time pitting Biden and Sanders against one another.

“Put your hand down for a second Bernie,” Biden said to his rival as he explained his support for building on ObamaCare, rather than scrapping it for "Medicare for All."

“I’m just waving at you Joe, saying hello,” Sanders retorted, before launching into his Medicare for All pitch.

That back and forth hit all of the notes on health care that have dominated the previous debates, with Biden warning that voters will be subject to higher taxes and Sanders insisting that the Medicare expansion is the only way to relieve the burden of health care costs for the working class.

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But Biden and Sanders were also pressed on the question of age — a lingering issue for both men.

Biden, who is 77, made news by demurring on a question about whether he’d commit to serving a second term as president if he’s elected.

“No, I won’t commit one way or another,” Biden said. “Let’s win this election then see where we are. Let’s see what happens.”

Sanders, who suffered a heart attack earlier this year, said age should not be a factor in who the party picks for its nominee.

“The issue is not old or young or male or female,” he said. “The issue is people standing up to take on the billionaire class.”