The biggest debate of the election cycle was chippy.

With 12 candidates vying for voters attention at Tuesday's debate in Westerville, Ohio, the White House contenders threw sharper jabs at each other and competed to outdo each other in their expressions of outrage over President Donald Trump.

Sen. Bernie Sanders returned to the debate stage two weeks after suffering a heart attack and resumed his call for a "political revolution." Billionaire activist Tom Steyer made his debate stage debut, but struggled to get much speaking time.

Here are some of the other big takeaways from Tuesday night's debate in suburban Columbus.

1: Biden addressed, but didn't quite blunt, Trump's smears on son's Ukraine business

Former Vice President Joe Biden didn't take any incoming fire from his Democratic rivals over Hunter Biden’s overseas business dealings, but he fell short of putting the issue to rest.

Debate blog:Elizabeth Warren takes rivals' shots, Joe Biden pivots on Ukraine and other top Democrat debate moments

Ahead of Tuesday night's debate, Biden vowed that he would not allow a family member or administration officials to be involved with foreign businesses should he be elected president. Hunter Biden acknowledged in a television interview that aired Tuesday that he probably wouldn't have been picked to serve on Ukraine energy company Burisma Holdings board if his last name wasn't Biden, but insisted he did nothing improper.

But asked directly by CNN co-moderator Anderson Cooper why it was OK for his son to serve on a foreign board when he was previously vice president but not if he wins the presidency, Biden didn't directly answer.

"Look, my son did nothing wrong," Biden replied. "I did nothing wrong. I carried out the policy of the United States government in rooting out corruption in Ukraine. And that's what we should be focusing on."

With each passing day, House Democrats receive more incriminating testimony in their ongoing impeachment inquiry of President Trump over his pushing Ukraine president Volodymyr Zelensky to investigate Hunter Biden’s business dealings in the Eastern European nation.

Trump, while damaged by the scandal, has managed to make Hunter Biden’s position serving on Burisma an ever-present issue in the campaign that shows no sign of disappearing. Biden has complained that the media has paid too much attention to his son’s business dealings, despite no evidence of impropriety.

The younger Biden did not have any past experience or technical background that would make him specially qualified to serve on the energy company’s board.

More:Hunter Biden will resign from board of Chinese firm, says he won't serve on foreign boards if Joe Biden elected president

In his Good Morning America interview, Hunter Biden pointed to his past service on the board of Amtrak as experience that helped qualify him for a job that reportedly paid $50,000 per month.

After Hunter Biden’s interview aired Tuesday morning, Trump took to Twitter to gloat, “Now Sleepy Joe has real problems! Reminds me of Crooked Hillary and her 33 deleted emails, not recoverable.”

The Bidens still have work to do to clear the murky waters Trump has created.

2: Surging Elizabeth Warren gets to feel sting of being a front-runner

Is it safe to declare Elizabeth Warren the co-frontrunner with Biden?

From the moment he entered the race in April, Biden — a well-known commodity with the imprimatur of his association with former President Obama — was the frontrunner in polls.

Recent polling suggests that has changed. Warren has come out on top in eight of the past 15 national polls, including a national survey by Quinnipiac University that showed her three percentage points ahead of Biden. It was the third Quinnipiac poll in a row where she’s led Biden.

But with her exalted status, the punches from her Democratic rivals are starting to get harder.

South Bend, Indiana, Mayor Pete Buttigieg hit hard early in the debate, hammering Warren for refusing to directly answer a question about whether Medicare for All would lead to a middle-class tax hike.

"Well, we heard it tonight, a yes or no question that didn't get a yes or no answer," Buttigieg said. "Look, this is why people here in the Midwest are so frustrated with Washington in general and Capitol Hill in particular. Your signature, Senator, is to have a plan for everything. Except this."

Warren retorted that overall costs will go up for the wealthy and for big corporations but down for middle class families.

“I will not sign a bill into law that does not lower costs for middle class families.” Warren said.

Sen. Amy Klobuchar also knocked Warren for how she’s gone about pushing her call for wealth tax, a plan that calls for a 2% hike on income for families making more than $50 million annually. Warren has said she would use the wealth tax to help fund tuition-free college, pay for universal childcare, and other programs.

“I want to give a reality check here to Elizabeth, because no one on this stage wants protect billionaires — not even the billionaire wants to protect billionaires,” said Klobuchar, referring to the billionaire candidate Steyer. “Your idea is not the only idea.”

Former Rep. Beto O’Rourke said he thought Warren's message is often too divisive.

“I think it’s part of the solution but I think we need to be focused on lifting people up and sometimes I think Senator Warren is focused on being punitive or pitting one side of the country against the other,” O’Rourke said.

Warren replied that she was "shocked at the notion that anyone thinks I'm punitive."

"Look, I don't have a beef with billionaires," she said. "My problem is you made a fortune in America, you had a great idea, you got out there and worked for it, good for you. But you built that fortune in America. I guarantee you built it in part using workers all of us helped pay to educate. You built it in part getting your goods to markets on roads and bridges all of us helped pay for. You built it at least in part protected by police and firefighters all of us help pay the salaries for."

3: Candidates are united in blasting Trump on Syria, but less robust in explaining how to undo the damage

The crowded field was unanimous as they ripped Trump’s abrupt decision to withdraw U.S. troops from northern Syria, turning the area into a powder keg where Russian forces are now looking to fill the security vacuum created by Trump.

“It’s been the most shameful thing any president has done in modern history in terms of foreign policy,” Biden said.

Buttigieg, who was deployed to Afghanistan as a Navy Reserve officer, said Trump betrayed Kurdish allies by acceding to Turkey's President Recep Tayyip Erdoganand allowing him to clear northern Syria of American-allied Syrian Democratic Forces who assisted U.S. troops in battling the terror group ISIS.

“What we were doing in Syria was keeping our word,” Buttigieg said. “Part of what makes it possible for the United States to get people to put their lives on the line to back us up is the idea that we will back them up, too. When I was deployed, not just the Afghan national army forces but the janitors put their lives on the line just by working with U.S. forces. I would have a hard time today looking an Afghan civilian or soldier in the eye after what just happened over there.”

The Democratic hopefuls were eloquent in their anger at Trump as they accused him of pushing the region to tumult. But they didn't offer much detail on how they would undo the damage.

Biden may have come the closest in offering a substantive answer to the question, saying he would work to safely return U.S. troops to northern Syria and look to put pressure on Erdogan and Syrian leader Bashar al-Assad.

"What I would do is I would be making it real clear to Assad that, in fact, where he's going to have a problem — because Turkey is the real problem here," Biden said. "And I would be having a real lockdown conversation with Erdogan and letting him know that he's going to pay a heavy price for what he has done now. "

4: The Biden vs. Warren rivalry got feisty

Soon after Biden entered the race in April, Warren took a swipe at him for his advocacy as a senator for the 2005 Bankruptcy Abuse Prevention and Consumer Protection Act, legislation that tightened rules on who could qualify for bankruptcy protection and benefited credit card companies.

"At a time when the biggest financial institutions in this country were trying to put the squeeze on millions of hardworking families who were in bankruptcy because of medical problems, job losses, divorce or death in the family, there was nobody standing up for them," Warren said. "I got in that fight because they just didn’t have anyone. And Joe Biden was on the side of the credit card companies."

Since then, the jousting between the moderate Biden and more liberal Warren had been otherwise anodyne.

That changed at Tuesday's debate.

Biden and Warren had a sharp exchange over who played what role in setting up the Consumer Financial Protection Bureau in 2010 following the national banking crisis two years earlier. Warren was the mastermind of the CFPB and helped the Obama administration stand it up.

Biden claimed that Warren wasn't crediting him with the role he played in getting the agency off the ground.

“I went on the floor and got you votes,” Biden told Warren. “I got you votes.”

Warren didn't acknowledge Biden’s remarks but thanked President Barack Obama.

“I am deeply grateful to President Obama for fighting so hard,” Warren said.

“You did a hell of job,” Biden offered.

“Thank you,” Warren said.

5: Septuagenarians make the case age is just a number.

Sanders returned to the campaign trail with Tuesday’s debate, an appearance that came just two weeks after he suffered a heart attack while campaigning in Las Vegas.

The moment was a big one for Sanders, 78, who as the oldest candidate in the field has frequently had to address the issue of whether his age will be an impediment should he be elected as president.

More:4 decades separate 2020's presidential candidates. Here's what that looks like.

He told co-moderator Erin Burnett that he was “feeling great,” and teased he would demonstrate his plan to continue his vigorous campaign with a big rally in New York City this weekend that would include a special guest. While the debate was still underway, news broke that Sanders had won the endorsement of Rep. Alexandria Ocasio-Cortez, who last year became the youngest woman elected to Congress and is a leading voice in the progressive movement.

But it wasn’t just Sanders who was asked to reassure voters that their age won’t be a problem.

Burnett noted in a question to Biden that former President Jimmy Carter said last month that he couldn’t have handled the duties of the presidency at age 80. Biden would turn 80 during his term should he win the White House.

“Look, one of the reasons I'm running is because of my age and my experience,” Biden said. “With it comes wisdom. We need someone to take office this time around who on day one can stand on the world stage, command the respect of world leaders, from (Russia’s President Vladimir) Putin to our allies, and know exactly what has to be done to get this country back on track.”

Warren, who would be 71 on Inauguration Day, batted away concerns about her age.

“Well, I say, I will out-work, out-organize, and outlast anyone, and that includes Donald Trump, Mike Pence, or whoever the Republicans get stuck with,” she said.

Rep. Tulsi Gabbard, 38, who is the second youngest candidate in the Democratic field, came to her septuagenarian rivals defense.

“I was going to say it's not fair to ask these three about their health and their fitness to serve as president but not every other one of us,” Gabbard said. “But here's the real question I believe you should be asking is: Who is fit to serve as our commander-in-chief? This is the most important responsibility that the president has."