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CLEVELAND, Ohio — The Trump campaign, already on shaky ground headed into this week's convention, struggled to find a response Tuesday to charges that Melania Trump’s prime-time speech lifted passages from Michelle Obama’s 2008 convention speech.

The side-by-side video of the two speeches, replayed endlessly on cable news, is jarring. A potential first lady describing her family’s values (“you work hard for what you want in life,” “your word is your bond,” “you treat people with respect”) in near-identical terms to a first lady whose own husband’s integrity, faith, and patriotism Donald Trump regularly throws into question.

“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.

Related: Did Melania Trump 'Rickroll' Us All?

"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."

Top Trump aide Paul Manafort responded erratically to the news, framing the story as overblown, as unimportant to the candidate, and later as part of a partisan conspiracy targeting Mrs. Trump.

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Manafort first told CBS News there was “no cribbing” of Obama's speech and minimized the issue’s relevance.

“Certainly there is no feeling on [Melania’s] part that she did it,” Manafort said. “What she did is use words that are common words.”

In an interview with NBC News later that morning, Manafort said Mr. Trump was “very pleased with last night.”

Later, Manafort accused Hillary Clinton of manufacturing the plagiarism story.

“It's just another example, as far as we're concerned, that when Hillary Clinton is threatened by a female, the first thing she does is try to destroy the person,” Manafort said.

The charge was odd given that Clinton and her top campaign officials had not commented on the plagiarism charge, which was first broken by journalist Jarrett Hill on Twitter.

"Nice try, not true, [Paul Manafort]" Clinton campaign spokeswoman Jennifer Palmieri tweeted in response to the accusation. "Blaming Hillary Clinton isn't the answer for ever Trump campaign problem."

Nice try, not true. @PaulManafort, blaming Hillary Clinton isn't the answer for ever Trump campaign problem. https://t.co/RvZ5GKeDYd — Jennifer Palmieri (@jmpalmieri) July 19, 2016

Trump’s former campaign manager Corey Lewandowski, who was fired after clashing with Manafort, said on CNN that whoever approved the speech should be “held accountable.”

“I think if it was Paul Manafort he would do the right thing and resign,” Lewandowski said.

It was not clear who in the Trump campaign bore responsibility for the speech. Mrs. Trump told TODAY’s Matt Lauer before her speech that she wrote her remarks “with as little help as possible.” But sources within the campaign said each family member was assigned a staff member to oversee their work and give a final sign-off and that her speech was considered the most important.

A statement by campaign spokesman Jason Miller early Tuesday morning credited the speech to a “team of writers” who worked with Mrs. Trump and acknowledged the remarks “in some instances included fragments that reflected her own thinking.”

New Jersey Governor Chris Christie, a top Trump surrogate, tried to take a glass half-full approach, telling TODAY that “93% of the speech is completely different than Michelle Obama’s speech.”

But national campaign co-chair Sam Clovis was less sanguine, telling MSNBC that the speech should have been run through anti-plagiarism software.

“I’m sure action will be taken inside the campaign to make sure it will never happen again,” Clovis said.

Perhaps the most creative defense of Mrs. Trump came from Republican National Committee spokesman Sean Spicer, who argued on MSNBC that the phrases in question were common enough to have been used by pop singers and cartoon characters.

“Melania Trump said, ‘You work hard for what you want in life,’ Akon said, ‘Work hard for what you get in life,’ John Legend said, ‘Work hard,’” Spicer said. “Melania Trump said, ‘the strength of your dreams and the willingness to work for them,’ Twilight Sparkle from My Little Pony said, ‘This is your dream, anything you can do dream.’”

Related: RNC Invokes 'My Little Pony' to Defend Melania Trump's Speech

That did not explain how the individual snippets lined up on after the other to mimic Mrs. Obama’s speech almost perfectly. John Legend wasn’t happy with the argument either. “I would very much like to be excluded from this narrative,” the singer tweeted.

While the campaign has yet to name the staffers responsible for writing and vetting the speech, the story has become an unwelcome distraction at the worst possible time. Trump, who trails behind Clinton in most general election polls and still faces challenges uniting the party, needs a successful convention to propel his candidacy to the next level.