Donald Trump is only extending his lead in a key early state - and there are some warnings signs for Ben Carson

With each passing week, Donald Trump's unyielding lead in the polls makes it increasingly clear that the real-estate magnate is not going anywhere.

A new WBUR poll released on Wednesday showed Trump continuing to hold a commanding lead among likely Republican voters in New Hampshire, the key first-in-the-nation primary state.

Trump actually ticked up a few points from when the last WBUR poll was conducted just more than two weeks ago. He rose to 23% in the latest poll, compared with 18% in the previous survey.

Sen. Marco Rubio (R-Florida) tied with retired neurosurgeon Ben Carson as the second most popular candidate in Wednesday's poll, garnering 13% support, with Sen. Ted Cruz (R-Texas) coming in fourth with 8%.

New Jersey Gov. Chris Christie (R), former Florida Gov. Jeb Bush (R), and Ohio Gov. John Kasich (R) all tied with 7% support.

Trump's consistent strength in the polls come as early polling data is starting to show some potential warning signs for Carson.

Though he remains one of the most favorable candidates in the race, Carson's favorability rating in New Hampshire has notably. The percentage of GOP voters in the state who view him favorably dropped from 63% in early October to 55% now, giving Rubio a slight edge as the most likable candidate among likely New Hampshire primary voters.

Many polling experts have speculated that Carson's support among Republicans may mirror the boom-and-bust arcs of previous insurgent candidates and could be a figment of the inability of early polling to predict actual results several months out.

"That softness of support for Carson might put him in a similar category as Michele Bachmann, Newt Gingrich, and Rick Santorum, all of whom rose to similar levels of support for several months, but then lost that support by the time voting started," Princeton polling expert Sam Wang told Business Insider recently. "Carson's rise has not yet lasted longer than they did."

Added statistics guru Nate Silver, the founder of the site FiveThirtyEight, in a discussion at Columbia University last weekend: "The polling doesn't become highly accurate until a couple weeks before Iowa sometimes or after Iowa, really."

But wary of Trump's resilience in the polls and the failure of almost every establishment-oriented candidate to gain traction, polling analysts also caution ruling out either candidate.

"The risk of something unusual happening is higher than usual. I think not as high as you'd gather from the press. I'd say the chance of Trump or Carson winning is probably 10% or lower, but still, you know, I'm not going to sit here confidently and say, 'Oh, it's impossible for them to win,' because the GOP may be a bit different than usual," Silver said.

Added Wang: "The hardening of support for Trump is extremely interesting and suggests that he might have staying power. His numbers have also lasted longer than those transient candidates from 2012. That puts him in a category more like Pat Buchanan in 1992 and 1996, who didn't get the nomination, but was a major force within the Republican Party."