Of all the promises Mitt Romney has made the past week in both campaign ads and on the trail, one of the statements that stood out was his promise to lower the unemployment rate from the current 8.1 percent to 6 percent after his first term in office.

In an interview Wednesday with Time magazine's senior political analyst Mark Halperin, the Republican presidential hopeful gave a number and a time period to be held accountable to his promise.

I can tell you that over a period of four years, by virtue of the policies that we'd put in place, we'd get the unemployment rate down to 6 percent, and perhaps a little lower, Romney said.

The promise, however, is not as bold as it sounds. The Congressional Budget Office predicted in a January report that the unemployment rate is already on its way down and will gradually decline to around 7 percent by 2015 and 5.5 percent by the end of 2017.

Obama campaign spokesman, Ben LaBolt, used the CBO report to criticize Rommney's 6 percent promise.

Government economists have been clear that under current law their projection today is that unemployment will hit 6 percent by that point, LaBolt said, according to CNN.

In a couple of campaign ads -- the most recent of which was released on Thursday -- entitled Day 1, Romney has listed a number of promises he would implement on his first day in office: repealing Obamacare, approving the Keystone pipeline and creating thousands of jobs, introducing tax cuts, deficit reductions, and standing up to China on trade.

He repeated those promises while defending his 6 percent unemployment claim on Fox News Thursday morning, saying a number of things would be responsible for the decreased rate.

You start off by saying, let's stop something that's hurting small business from creating jobs and that's 'Obamacare.' Get rid of it, Romney said. No. 2, have an energy strategy that takes advantage of our natural gas and oil and coal, as well as our renewables. Those low cost energy fuels will ultimately mean jobs come back here, even manufacturing jobs that left here. And finally, get a handle on the deficit so that people understand if they invest in America, their dollars will be worth something in the future.

It's not the first time Romney has made the promise. At a North Las Vegas truck dealership in September, the former Massachusetts governor vowed to lower the unemployment rate from the then-9.1 percent to 5.9 percent in four years, according to ABC News.