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Santorum goes up with radio ad

Here come the ads by the GOP presidential hopefuls...

Rick Santorum becomes the first Republican presidential candidate to air an ad -- a 60-second radio one.

The ad's message is on government spending. "Someone has to have the courage to tell the American public, 'We can't afford the government we have right now, and we need to cut it back across the board."

Per the campaign, it will begin airing on Monday on satellite radio, and then later in the week in Iowa, New Hampshire, and South Carolina.

Santorum will appear at Monday's GOP debate in New Hampshire.