"Melania has been humiliated. No doubt heads are going to roll."

“Not paying attention to details — that costs elections,” a source close to the campaign, who requested anonymity to speak freely, told NBC News.

The mistake is poised to cause turmoil within the campaign as well. Campaign sources described Mrs. Trump’s speech as the most sensitive of the convention because of her extreme discomfort with the political spotlight — she rarely gives interviews or appears at rallies and did not attend last week’s event introducing Indiana Gov. Mike Pence as her husband’s running mate.

Mr. Trump, who praised her “absolutely incredible” speech on Twitter last night, is unlikely to tolerate an error that cuts so close to his relationship with his wife.

“It’s piss-poor staff work,” a source within the campaign told NBC News. “Melania has been humiliated. No doubt heads are going to roll.”