For the first part of the debate, Obama was impatient and condescending, as if he did not understand why he would be required to prove his obvious superiority. Halfway through the evening, he caught his mistake and began to smile instead of glare and treat Romney more respectfully. It may be that Obama's repeated muttering and groaning under his breath will become the equivalent of Al Gore's sighing. It cannot be long before someone strings all of Obama's grunts and harrumphs together and it goes viral.

As Romney took command, Obama seemed to find his opponent's aggressiveness surprising. It was good news for Romney that the moderator demonstrated total control of the debate. The even better news was that the moderator was, effectively, Romney. Jim Lehrer let the two gladiators go at each other with minimal interruption and created one of the best debates on record. The nation got to see two grown men debating the issues respectfully but forcefully. That's what debates used to be and still should be. A more self-important performance by Lehrer might not have permitted Romney to demonstrate that he had the strength to take on the leader of the free world and command the night.

Romney did not just win on style; he won on substance. He punched through with a simple, clear and direct five-point plan to grow the economy. He presented it as an alternative to President Obama's failed expansion of what he called "trickle-down government." Now we know what Romney is for and what he is against. That's the beginning of a narrative that can explain why the next four years under Romney would be better than the last four under Obama.

Over the next few days, Team Obama will try move on from this debate, acknowledging that their candidate didn't take it seriously enough, was too busy keeping the economy paralyzed and promising that he'll be better next time. But Round 1 goes to Mitt Romney. Taking on a sitting president mano-a-mano, without being intimidated by the man or the office, takes brass. Mitt Romney displayed that tonight.

Alex Castellanos, a CNN contributor, is a Republican consultant and the co-founder of Purple Strategies. Follow him on Twitter: @alexcast.

Julian Zelizer: The "truthiness" debate

This was a debate that will keep the fact checkers busy for days. Each candidate tried to avoid any big mistakes and to undercut the basic claims of his opponent, suggesting to voters in the swing states that what you see is not what you will get.

Both men showed that they were in command of the major policies, with the debate at times sounding more like a discussion at a Washington think tank than the kind of rough-and-tumble campaign scenes voters are accustomed to.

President Barack Obama used much of his time to hammer away at Romney's proposed fiscal policies, claiming that the former governor is really a champion of trickle-down economics that would benefit the rich and do little to curb the deficit. Obama sought to connect himself to President Bill Clinton and the booming economy of the 1990s, and to tie Mitt Romney to President George W. Bush and the financial collapse of 2008.

Romney, while insisting that his programs would help the middle class, went on the offensive by questioning the veracity of the president. At one point, comparing Obama to his sons, he claimed that the president was misrepresenting his policies and spreading information that is not true. Hammering away at the state of the economy, Romney made his basic argument clear when, recounting what he heard from a friend, he said to Obama, "You don't just pick the winners and losers, you pick the losers."

Overall, this didn't seem like a game changer. Romney probably benefited the most as he seemed energized, engaged and brought the debate back to the laggard economy, away from his gaffes. Obama, playing defense and waiting for Romney to make mistakes, was able to reiterate his basic campaign theme that Romney is a step backward toward 2008 and that he is someone who will protect basic programs that will help the middle class.

Julian Zelizer is a professor of history and public affairs at Princeton University. He is the author of "Jimmy Carter" and of the new book "Governing America."

Bob Greene: Two smart men take on substance

"You've been president four years."

Had Barack Obama, during the autumn of 2008, been able to look four years into the future and somehow seen someone, accurately, saying those words to him in 2012, he undoubtedly would have been thrilled.

But on the Denver debate stage Wednesday night, when Mitt Romney spoke those words to Obama, they sounded like an admonition.

Viewers hoping for crudely hurled insults, for zingers meant not just to sting but to wound, were likely disappointed. For years, the public has complained that presidential politics have become too petty and trivial; the plea has been: "Why can't the candidates talk about serious issues?"

Well, that's what the public got. The phrase "Dodd-Frank" was spoken so many times that you'd have half-thought it was an attack-ad punchline, not the name of a bill dedicated to Wall Street reform. Regardless of your political preferences, what you saw Wednesday night was two smart men talking about things they consider important to the country's future. Was it at times dull? Maybe. Was the dullness, in an unexpected way, kind of refreshing? You can make the argument that it was.

About 20 minutes into the debate, during some byplay between Obama, Romney and moderator Jim Lehrer, Romney said:

"It's fun, isn't it?"

The kind of policy-oriented talk that dominated the proceedings probably really is fun for Obama and Romney. And perhaps that's not such a bad thing. One of them will be running the country for the next four years. Seriousness may not be scintillating, but it can be reassuring to witness it once in a while.

Hilary Rosen: Romney's revisionist history

Honestly, I think I am more impressed with President Barack Obama tonight than I have ever been, because if I were on that stage I would not have been able to resist screaming at Mitt Romney for his repeated revisionist history on his own positions, for his distortion of the president's record and for the smirk on his face while he was doing it.

On taxes: Romney said that he wasn't going to cut taxes because he'd close loopholes, but he wouldn't say which loopholes he'd close. And then he denied that the tax cut extension contributes to the deficit.

On health care: Romney disingenuously suggested that he has a plan that will provide people with the same good benefits of Obamacare. He doesn't have such a plan. Romney says his plan deals with pre-existing conditions, but it would only keep insurers from taking away coverage, doing nothing for Americans with pre-existing conditions who are not able to get an insurance plan. As a result, 72 million people would be unable to obtain insurance, more than if Obamacare had never been passed.