JERSEY CITY, N.J. (CBSNewYork)New Jersey Gov. Chris Christie is on the stump, campaigning for Republican presidential hopeful Mitt Romney in the key battleground state of Ohio for a few days.

The campaign may be in the home stretch, but Christie warned there is still plenty of time left for momentum shifts.

WCBS 880’s Marla Diamond with Gov. Christie in Jersey City

“Things will go up and down, you’ve got 28 days to go until this election. It will change a number of times again, in my view,” Christie told WCBS 880’s Marla Diamond before heading to the Buckeye state.

Christie said his number one piece of advice to Romney is to stay true to himself.

“The American people can tell really quickly if you’re trying to be something different. So you know what? I think the challenge for Governor Romney and the challenge for the President is be yourself and let the American people judge you,” Christie told Diamond.

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And though Romney enjoyed a bump in the polls from his first debate performance, Christie said Romney would be wise not to rest on his laurels.

“The President of the United States is a formidable political force and you underestimate him at your own risk,” added Christie.

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