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Marco Rubio’s stumble in Saturday’s Republican debate wasn't just the Florida senator repeating the same phrase four times, that President Obama “knows exactly what he’s doing."

Rubio in effect declared himself an advocate of a controversial view of President Obama.

For the last eight years, conservatives have alternated between two competing theories on why they so strongly disapprove of Obama’s presidency: One is that Obama, lacking sufficient governing experience before entering the Oval Office, is simply incompetent, unable to manage affairs at home and constantly out-witted by foreign leaders.

The other theory from conservatives is that Obama ran in 2008 as a moderate, but was hiding his true agenda to push the country aggressively to the left.

In this view, Obama has been almost too competent, accomplishing goals that conservatives hate.

Related: Four Takeaways From the New Hampshire GOP Debate

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There is evidence for both theories. The glitch-filled launch of healthcare.gov, the failures of the Veterans Administration and the struggles to find coherent policies on Syria and ISIS have showed a president at times not managing the government well.

But on a long list of issues, from the 2009 stimulus to the Iran nuclear deal, Obama and his team accomplished very complicated projects, smartly outmaneuvering conservative opponents to enact liberal goals.

Rubio, in the debate, strongly advocated the second theory.

"Let's dispel once and for all with this fiction that Barack Obama doesn't know what he's doing. He knows exactly what he's doing. Barack Obama is undertaking a systematic effort to change this country, to make America more like the rest of the world," Rubio said.

"That's why he passed Obamacare and the stimulus and Dodd-Frank and the deal with Iran. It is a systematic effort to change America," Rubio added.

New Jersey Gov. Chris Christie was in the initial exchange with Rubio, but Donald Trump had the strongest rebuttal to the Florida senator.

"Marco said earlier on that President Obama knows exactly what he's doing, like we have this president that really knows. I disagree, respectfully, with Marco," Trump said. "I think we have a president who, as a president, is totally incompetent, and he doesn't know what he's doing."

"I think he has no idea what he's doing. And our country is going to hell," Trump added.

Trump and the three former or current governors, Florida’s Jeb Bush, Ohio’s John Kasich and Christie, have a strong incentive to adopt the "Obama is incompetent" narrative. They are running as the candidates with management experience — Trump in business, the governors at the state level.

The 44-year-old Rubio has just as big a need to make the case that a young senator can manage the government well, as long as he has the right ideals.

Ted Cruz, who is five months older than Rubio and also in his first term in the Senate, avoided this topic in the debate, but has also leaned toward the "Obama as radical liberal" narrative.

Republicans often vacillate between these two theories, blasting Obama for his executive orders on immigration (Obama as radical) and at the same time saying he can't defend the American border (a competence question).

Bush, Christie, Kasich and Trump can make both charges at the same time. Cruz is running as the candidate most in line with conservative ideologues, so his backers are not looking for governing experience as much as signals he is to the right of the other candidates.

But Rubio is trying to reach voters who might otherwise back one of the governors. And the Florida senator has the problem of never having held an executive job — like the president he is trying to succeed.