"He's had a tough couple of weeks, let's be honest," Christie said of Romney on Face The Nation.
"But there's great news for Republicans. We have a candidate who's going to do extraordinarily well Wednesday night. . . . He's going to lay out his vision for America, he's going to contrast what his view is with what the president's record is, and the president's view for the future. And this whole race is going to be turned upside down come Thursday morning."
Christie said the first presidential debate, intended to focus on domestic affairs, has the power to change several polls that show President Obama's narrow lead widening.
"Tens of millions of people really for the first time will be tuning into this race," Christie said on Meet The Press. "This race will really start to tighten and move in Gov. Romney's direction."
Repeatedly asked to acknowledge the political problems caused by Romney's dismissal of 47 percent of the electorate in a now-famous gaffe, Christie changed his argument from a few weeks ago, when he blamed reporters for perpetuating the story. This time, he said the American people don't care about what Romney said.
"They know political candidates at times when they're being taped are going to say things inartfully," Christie said on Face The Nation, comparing it to the time in 2008 when Obama mistakenly said there are 57 states in the country.
Christie dodged questions about whether Romney would raise taxes as part of a bipartisan spending cut deal. Asked to explain why Romney hasn't offered more specifics about his economic recovery plan, Christie argued that Obama has been even more vague. In one of several critiques on the media Sunday morning, he said on Meet The Press: "I wish you guys were just as tough on the president."
"The president's just trying to run out the clock," Christie added on Face The Nation. "He desperately wants to run out the clock with platitudes that sound nice."
The Obama campaign released a statement Sunday responding to the governor's accusations: "Contrary to Christie's rhetoric, President Obama has laid out specifics for how he'd achieve these objectives - from tax reform proposals to encourage manufacturers to create jobs here and not overseas, to a budget plan that has been independently scored by the Congressional Budget Office."
(The CBO concluded in March that the president's budget would add less to the national debt than if lawmakers simply extended a number of favored policies, such as the Bush-era tax cuts, according to CNNMoney.)
While Christie touted the expected debate performance, Romney's running mate, Rep. Paul Ryan, did the opposite. He worked to keep debate expectations for Romney in check, praised Obama's debating skills, and called the Democratic incumbent "a very gifted speaker" with years of experience on the national stage. He played down signs that Obama was gaining distance in the most competitive states. Polls are tight, Ryan said, and will stay that way until the election Nov. 6.
"We're running against an incumbent president with incredible resources," Ryan said. "More importantly, I don't think one event is going to make or break this campaign."
Ryan said on Fox News Sunday that the debate would mark Romney's debut "on this kind of stage." Romney participated in more than two dozen multi-candidate debates during White House runs in 2008 and 2012, and went one-on-one against Sen. Edward M. Kennedy (D., Mass.) during a losing 1994 Senate bid.
"They expect to come out of this with the race fundamentally changed. Now, what does that mean?" asked David Plouffe, a senior White House adviser, on Meet the Press. "If it's going to fundamentally change, that means in seven or 10 days from now you'll see states like Ohio tied, the state of Iowa tied because that's what really matters here. So they have set the bar quite high."
Ryan acknowledged errors by the campaign but urged Republicans who are publicly carping to join him on the trail to witness the forceful case they're making.
"We've had some missteps, but at the end of the day, the choice is really clear," Ryan said, adding that until now, he and Romney "have not been able to frame that choice as clearly."
On Sunday, Obama headed to Las Vegas for an evening rally and planned to stay in Nevada as he prepared for the debate. Romney remained in Boston, going through preparations of his own.
This article contains information from the Associated Press.