Will Ben Carson be able to recover from a bad month?

Donald Trump has by now demonstrated that he’s not merely another fad candidate in the Republican presidential race. Dr. Ben Carson, on the other hand, still has a lot to prove.

At the start of the month, Carson overtook Trump in the national polling average and in the key early states of Iowa and South Carolina. He also moved into a close second behind Trump in New Hampshire. And he seemed to have the potential to rise higher, with Republicans giving Carson the highest marks of any candidate — by far — on personal favorability.

But with this rise to the top has come a new level of scrutiny from the press and from his opponents. And there are now clear signs that Carson is not holding up well under the spotlight.

RELATED: Could the Paris attacks contribute to derailing Ben Carson’s lead?

Three weeks ago, an NBC News/SurveyMonkey online poll showed Carson tied with Trump at 26%. But now the poll shows that Carson has fallen 10 points behind Trump and is tied for second place with a surging Ted Cruz. There is evidence of slippage elsewhere, too.

In New Hampshire, Carson pulled within two points of Trump in a WBUR poll at the start of the month. But this week, that same poll shows Carson falling back to 13%  – 10 points behind Trump and tied with Marco Rubio. A new Fox News poll in the Granite State has Carson at just 9% – tied for fourth with Jeb Bush.

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The NBC News/SurveyMonkey poll paints a clear picture of what’s happening: At the heart of Carson’s rise has been the support of white evangelical voters, who hold particular sway in Iowa (where they accounted for nearly 60% of all caucus-goers in 2012) and South Carolina (where they made up 64% of the 2012 primary electorate). At the start of this month, Carson was comfortably ahead with white evangelicals, netting 33% of their support. But in the last three weeks, Carson has lost a quarter of that support. At the same time, Cruz has leaped from 7% to 22% among white evangelicals — pulling into a virtual tie with Carson and Trump.

The movement is even more striking with Republicans who describe themselves as “very conservative.” With this group, Carson’s support has been sliced in half in the last three weeks, from 30% to 15%, while Cruz has jumped from 25% to 40%.

The impetus for this decline isn’t entirely clear. Aspects of Carson’s life story, which has been crucial to his appeal to religious conservatives, have been challenged by several press reports this month. But Carson dismissed these as ideologically motivated attacks from the liberal media, and conservative leaders and press outlets largely stuck by him. Still, even if that didn’t turn Republicans against Carson personally, the episode may have caused some of them to doubt the wisdom of nominating him for president.

RELATED: Carson aides admit candidate needs work on foreign policy

There’s also the matter of the Paris attacks, which have refocused the GOP debate on national security, a topic Carson has struggled to show a command of. And there’s the simple fact that Cruz — with two well-received debate performances and a major endorsement from Iowa Rep. Steve King — has had a very good month.

Add it up and there are real questions about Carson’s durability as a leading contender. Yes, more numbers are needed. Maybe there will be other national polls in the next few weeks that show Carson back at or near the top. And maybe he’ll retain enough evangelical support to remain in the game in Iowa through the caucuses. But his slippage this month is notable.

Just compare Carson’s trajectory to that of Trump, who took the lead in the Real Clear Politics national polling average a month after entering the race in June and then held it — through countless predictions of his imminent demise — for the next 107 days. Then, early this month, Trump lost that lead to Carson, only to reclaim it after three days. And he’s held it ever since. Trump has shown the ability to hold the lead through intense scrutiny and turmoil. Carson has not done that this month.

Ben Carson, Donald Trump, Election 2016 and Polling

Will Ben Carson be able to recover from a bad month?