Online poll: Carson slips, leaving Trump on top

Retired neurosurgeon Ben CarsonBenjamin (Ben) Solomon CarsonDetroit school board considers dropping Ben Carson’s name from local high school Number of homeless vets declined in last year Overnight Energy: Chief energy regulator vows to steer clear of political fights | Zinke was referred to DOJ shortly before watchdog controversy | Groups threaten to sue EPA over paint stripper MORE has slipped in a new NBC News/Survey Monkey online poll, leaving celebrity businessman Donald TrumpDonald John TrumpBroward County official Brenda Snipes submits resignation after criticism Retired lieutenant general tears into Trump over attacks against Navy SEAL: 'Disgusting' Senate barrels toward showdown over Trump's court picks MORE alone again at the top of the Republican presidential field.

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Trump holds the top spot at 28 percent among Republican and Republican-leaning independents, while Carson has dropped 8 points from the same online survey conducted last month. Online surveys are generally considered less scientific.

That puts Carson neck-and-neck with Sen. Ted CruzRafael (Ted) Edward CruzDem gains put Sunbelt in play for 2020 Reelection campaign starts now, like it or not Rise of big cities push Texas to swing-state territory — maybe by 2020 MORE (R-Texas) at 18 percent in the new poll. Sen. Marco RubioMarco Antonio RubioHillary advisers battle over whether she’ll run in 2020 Rubio defends '3 point kick' analogy: 'You think everyone who follows politics knows what a field goal is?' Lawmakers to introduce bipartisan bill targeting China's treatment of Muslims MORE (R-Fla.), another top contender, follows at 11 percent.

Cruz, who has pushed back hard against allowing Syrian refugees into the U.S. after the terror attacks in Paris, now leads among those who identify as "very conservative" at 40 percent, beating both Carson (15 percent) and Trump (28 percent).

Rubio and Cruz have sparred since the the fourth GOP debate last week on issues of illegal immigration and national security, while Trump has seen leads in several other polls after the Paris attacks.

Meanwhile, former Florida Gov. Jeb Bush stands at 4 percent in the latest survey, while New Jersey Gov. Chris Christie and former Hewlett-Packard CEO Carly Fiorina take 3 percent each.

The online poll of 2,440 Republican and Republican-leaning voters was conducted Nov. 15-17 with an estimated margin of error of 2.9 points.