Florida senator and Republican presidential candidate Marco Rubio told Megyn Kelly tonight that he's not as concerned about his dipping poll numbers as he is about communicating his message to the American people.

"This is a great country, and it can be greater. That's what this campaign is about," Rubio said.

He added that he's ready for the big stage of tomorrow's Fox News debate, and he understands the magnitude of the event.

What's the one thing you want people to take away about Marco Rubio? Megyn asked.

"I have a debt to this country I'll never repay," Rubio said, explaining that he's running for president because he wants America to continue to be a country where parents can do for their children what his parents did for him.

"The purpose of my parents' life was to give me the chance to do all the things they never could. That makes us different from the rest of the world. And the reason I'm running for president is I want this to continue to be that kind of country."

Watch the "Kelly File" clip above.

Don't miss the Fox News-Facebook Republican presidential debate, Thursday August 6, live from Cleveland, Ohio at 8:50p ET, moderated by Megyn Kelly, Bret Baier and Chris Wallace.

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