Washington (CNN) The race to win the backing of some of the GOP's most prominent mega-donors will end in a stalemate this month.

Charles and David Koch have not cut a check to any of the Republican presidential hopefuls, according to a person familiar with their political activities. Nor do the brothers plan to jump into the fray ahead of a June 30 fundraising deadline that has candidates scrambling for cash.

Those campaign finance reports, which will become public in July, offer the first snapshot of how donors are lining up behind Republicans now that the field has expanded to include more than a dozen contenders.

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