By JILL COLVIN, Associated Press

NEWARK, N.J. (AP) — Donald Trump's campaign for president will begin airing radio ads on Thursday in the three earliest-voting states, marking the first time the billionaire businessman has spent money on paid advertising since he launched his bid.

Trump's team announced Wednesday that its first two radio ads will run through the end of November in Iowa, New Hampshire and South Carolina. It says the ad buy is valued at $300,000.

The spending comes as Trump continues to adjust to the new realities of an evolving campaign in which he is no longer the undisputed front-runner of the Republican field. While he remains on top in many opinion surveys, retired neurosurgeon Ben Carson has surged past him in others. And candidates like Florida Sen. Marco Rubio and Ted Cruz of Texas are drawing new attention from voters and donors as the opening contests near.

On Wednesday, Trump told reporters in New Hampshire, where he officially filed to appear on the state's primary ballot, that the ads would be "very, very positive, about good things and great things about the country."

But he added a warning to rivals who may be considering negative ads against him. "If they hit me, they will get smacked like they never got smacked before," he said.

Trump has so far spent little of his own fortune on his campaign, relying mainly on donor contributions to fund his operation and on the news media to promote his message.

Trump often brags that he'd originally expected to spend $20 million or $25 million for ads by this point in the campaign, but hasn't needed to because he's doing so well. He's continuing to holding back on television ads, which are significantly more expensive than radio.

Trump campaign manager Corey Lewandowski declined to discuss which firm had produced the radio ads, saying the information would be contained in the campaign's next financial disclosure report.

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Associated Press writer Holly Ramer in Concord, New Hampshire, contributed to this report.