With three weeks until Election Day and their third and final debate focused on foreign policy and national security next week, it was their last opportunity to go head to head on the economy and other domestic issues.
Here are five things we learned from Round Two:
1. The old Romney rears his head
Romney has a knack for hurting himself.
He's has been stung by his self-inflicted wounds throughout the 2012 campaign ("I'm not concerned about the very poor" springs to mind).
The GOP nominee stumbled into a few messes of his own making on Tuesday.
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Just after the debate began, Obama landed a clean hit on Romney over his opposition to the federal bailout of Chrysler and General Motors.
Instead of letting the moment pass and moving on to the next question, Romney decided to once again relitigate the auto bailout, a measure supported by a large majority of voters in the presidential battleground of Ohio.
"He said that I said we should take Detroit bankrupt," Romney said. "And that's right. My plan was to have the company go through bankruptcy like 7-Eleven did and Macy's and Continental Airlines and come out stronger."
The end result? When he had a chance to mitigate the damage, Romney instead reminded millions of viewers that he would have let the auto industry go under without government help. As the saying goes: When you're explaining, you're losing.
Later, Romney got into a series of nit-picky squabbles with moderator Candy Crowley over the mechanics of the debate -- the order of questions, equal time and the like.
It didn't sound bold or presidential, and it called to mind Romney's helpless appeal to Anderson Cooper during a 2011 Republican primary when Rick Perry kept interrupting him.
Then there was his finale, when he seemed to allude to his cringe-inducing remarks about 47% of Americans as people dependent on government who refused to take personal responsibility.
"I care about 100% of the American people," Romney said. "I want 100% of the American people to have a bright and prosperous future."
Obama, inexplicably, had not mentioned the 47% comments all night. But it seemed as if Romney had given him a reminder, and Obama promptly teed off on the secretly taped fundraising comments when his turn to speak came around.
2. Republicans see an opening on Libya
It was one of Obama's brightest moments of the night.
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He sternly turned to Romney, who had just accused the president of misleading voters about the terrorist attack on the U.S. mission in Libya that killed four Americans, and essentially told him: How dare you.
"The suggestion that anybody in my team, whether the secretary of state, our U.N. ambassador, anybody on my team would play politics or mislead when we've lost four of our own, governor, is offensive," Obama said. "That's not what we do. That's not what I do as president, that's not what I do as commander in chief."
Points for the president.
But Obama's insistence that he called the Benghazi tragedy a terrorist attack from the outset still drew scorn from Romney, who said the administration had actually blamed the attack on a mob incited by an anti-Muslim YouTube video.
After the debate, Romney advisers made an issue of the administration's varying answers on Libya and vowed to push it in the coming days.
They circulated talking points to campaign surrogates, highlighting Obama's speech to the United Nations in which he seemed to blame the attack, in part, on a mob and not terrorists.
"What has happened is a perceived advantage for the president on foreign policy has been reversed because of what happened in Benghazi and how the president responded to it," Ohio Sen. Rob Portman, a Romney confidant, told reporters after the debate. "The issue was an issue that was to the president's favor. He was someone that was more respected on foreign policy as of a couple weeks ago. That has changed now."
But how much will Libya resonate with voters who place the economy atop their list of concerns?
Even Portman acknowledged that foreign policy only ranks "probably 7 or 8 or 9" on the list of issues voters deem important. Still, he argued, it's one more chink in the armor for a president running neck-and-neck with his challenger.
3. Obama throws the briefing book at Romney
If Obama didn't glance at his briefing book before the Denver debate, he definitely did this time.
From the outset, Obama sounded like he was sending a bouquet to his rapid response team in Chicago, a group of hard-charging staffers that pushes anti-Romney stories to campaign reporters on a daily basis.
Answering the first question of the debate, which was about jobs, the president unloaded on the Republican nominee, saying, "when Governor Romney said we should let Detroit go bankrupt, I said we're going to bet on American workers and the American auto industry and it's come surging back."
That was soon followed by a scathing attack on the former Massachusetts governor's signature economic plan.
"Governor Romney doesn't have a five-point plan. He has a one-point plan. And that plan is to make sure that folks at the top play by a different set of rules," claimed Obama.
And the president attacked Romney's proposals to reform taxes and lower the deficit.
"Governor Romney was a very successful investor. If somebody came to you, governor, with a plan that said, 'Here, I want to spend $7 or $8 trillion, and then we're going to pay for it, but we can't tell you until maybe after the election how we're going to do it,' you wouldn't take such a sketchy deal and neither should you, the American people, because the math doesn't add up."
Then there was this zinger on outsourcing: "Governor, you're the last person who's going to get tough on China."
Obama also criticized Romney over the rate he pays on his federal taxes, his stance on health care coverage for contraception and his calls to cut federal funding for Planned Parenthood, his plans to reform Medicare, and his support of Arizona's controversial illegal immigration law. The reference to Romney's "47%" controversy came just before the closing bell.
The president sure seemed like he was trying to make up lost ground following his lackluster performance in the first presidential debate two weeks ago.
The Obama campaign claimed victory.
"You saw Governor Romney backpedaling all night, you saw him defensive, in some cases stammering, trying to explain his plans," senior Obama campaign adviser David Axelrod told reporters after the debate. "It was a dominant performance because the president pulled the curtain back on this bait-and-switch of Mitt Romney."
The Romney campaign disagreed.
"I think President Obama came in and overcompensated," senior Romney campaign strategist Stuart Stevens said. "There's a difference between showing passion and showing you having a plan."
What did people who watched the debate think?
By a 49%--35% margin, debate watchers questioned in a CNN/ORC International poll said that Obama spent more time than Romney attacking his opponent. And nearly three-quarters said the president performed better than expected.
Maybe the president took note of Vice President Joe Biden's aggressive debate performance in last week's vice presidential showdown with GOP runningmate Rep. Paul Ryan. Regardless, we learned that Obama was able to step it up when it mattered the most.
4. These guys don't like each other very much
It's pretty obvious -- Obama and Romney don't like each other.
Need more proof?
The second debate provided plenty of examples.
The two candidates stood toe-to-toe and clashed over domestic oil production.
"Governor, we have actually produced more oil," said Obama.
"No, no. How much did you cut licenses and permits on federal land and federal waters?" asked Romney.
"Governor Romney, here's what we did. There were a whole bunch of oil companies," responded Obama.
"No, no, I had a question and the question was how much did you cut them by?" interrupted Romney
"You want me to answer a question," fought back Obama.
"How much did you cut them by?" asked Romney again.
"I'm happy to answer the question," fired back Obama.
Another heated exchange between the candidates ended with Romney pushing back at an interruption by the president by saying, "You'll get your chance in a moment but I'm still talking."
That moment brought gasps from some in the audience.
Republican strategist and CNN contributor Alex Castellanos described the debate as a clash between "two high school jocks who didn't like each other very much."
5. Romney has binders full of women
It was your Internet meme of the night.
Asked about his support for women in the workplace, Romney recalled the hiring process he implemented after becoming Massachusetts governor.
"We took a concerted effort to go out and find women who had backgrounds that could be qualified to become members of our cabinet," Romney said. "I went to a number of women's groups and said, 'Can you help us find folks,' and they brought us whole binders full of women."
Binders. Full of women!
The strange turn of phrase quickly became a trending topic on Twitter and the title of a brand new Tumblr blog mocking the Republican nominee's awkward word choice.
Beyond the jokes, the answer called attention to Romney's tightrope walk on a sensitive issue for women.
During the Republican primaries, Romney refused to say whether he would have supported the Lilly Ledbetter Fair Pay Act, the first bill Obama signed into law. His campaign later said it wouldn't support the repeal of the law -- hardly a ringing endorsement.
So on Wednesday, when asked about equal pay, Romney resorted to personal anecdotes about women he once hired and promised to fix the economy so more women can find jobs.
Obama, like he did all night, pounced.
"When Governor Romney's campaign was asked about the Lilly Ledbetter bill, whether he supported it, he said I'll get back to you," Obama said. "That's not the kind of advocacy that women need in any economy."
By Peter Hamby and Paul Steinhauser
ChiboyChuks Opinion: I feel Obama is gonna run the second term.