$300 million worth of ads have hit voters ahead of the first GOP primary contests

Republican presidential candidate Nikki Haley arrives at a campaign event at the Olympic Theater in Cedar Rapids, Iowa, on Thursday. The state's caucuses will be held on Monday. (Anna Moneymaker/Getty Images)

Almost $300 million has been spent to try to win the Republican presidential nomination so far, two-thirds of it in the first two nominating states, Iowa and New Hampshire, according to data analyzed by NPR and compiled by the ad-tracking firm AdImpact.

Most of that money is coming from super PACs and outside groups.