Republican presidential frontrunner Donald Trump took to Twitter — as only he does — Friday threatening to sue his chief rival Texas Sen. Ted Cruz "for not being a natural born citizen," unless he meets three conditions.

Though vague, Trump's first condition is that Cruz "clean up his act" on the campaign trail. Then, he says the Texas senator needs to "stop cheating," most likely referencing the Iowa dustup over the Cruz campaign's claim that GOP presidential hopeful Ben Carson was dropping out, which Cruz has since apologized for.

Lastly, the outspoken billionaire businessman called on Cruz to drop the "negative ads," many of which target Trump.

If @TedCruz doesn’t clean up his act, stop cheating, & doing negative ads, I have standing to sue him for not being a natural born citizen.

— Donald J. Trump (@realDonaldTrump) February 12, 2016

If Cruz does not comply with Trump's conditions, the billionaire says, "I have standing to sue him for not being a natural born citizen."

Cruz and Trump are currently competing in South Carolina for the No. 1 spot. The latest polling shows Trump with 36 percent of the vote, followed by Cruz with 20 percent.

The South Carolina Republican primary will take place Saturday, Feb. 20.

—

Follow the author of this story on Twitter:

Follow @tregp