Donald Trump has been overtaken in a key polling average for the first time in 4 months

Retired neurosurgeon Ben Carson now leads real-estate mogul Donald Trump in the Real Clear Politics polling average, marking the first time since mid-July that Trump has been out of the top position.

The site averaged the results of four recent polls, including Wednesday's Quinnipiac survey that showed the two Republican outsiders in a virtual tie for first place.

According to the average of the four polls, Carson gets 25.3% of the vote to Trump's 24.3%.

It's the first time since July 19, when Trump was running second to former Florida Gov. Jeb Bush (R) in the average, that he has not led.

Carson has surged in Republican primary polls in recent weeks, gaining on Trump both nationally and in the first-caucus state of Iowa. Nationally, the two candidates appear to be very evenly matched — both Trump and Carson lead in two of the four surveys included in the average.

Though Carson has taken the lead in Iowa, Trump still has dominant leads in the other early-voting states of New Hampshire, South Carolina, and Nevada.

For his part, the real-estate magnate has gone on the offensive against Carson amid his surge. That included Tuesday interviews and a book-signing event at Trump Tower, during which he suggested Carson didn't have the "temperament" to be president.

"It's not his thing. He doesn't have the temperament for it," the New York real estate mogul told ABC News' George Stephanopoulos on "Good Morning America." "I think Ben just doesn't have the experience."

Behind Carson and Trump, Sen. Marco Rubio (R-Florida) has risen to third place in the average with 11% support. He's followed by Sen. Ted Cruz (R-Texas) at 8.3% and Bush at 6.3%.

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See Also:

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