GOP presidential hopeful Donald Trump on Thursday declared that fellow front-runner Ben Carson was suffering a "free fall" and then went on to claim credit for his rival's alleged demise.

"I think [Carson's campaign] is in free fall, I think, if you look over the last week and a half, two weeks," the real estate tycoon assessed at a rally in the key early-caucus state of Iowa, CNN reported. "Maybe I helped it along by making a speech two weeks ago."

The statement was an apparent reference to what the news channel's Theodore Schleifer called a "95-minute tirade" last week, in which Trump had insulted Carson supporters as "stupid."

The description of a campaign in demise, meanwhile, followed a slight decline in the polls for Carson, who in the past few days had made headlines with a controversial remark about refugees and with a report about his troubles understanding the complexities of U.S. foreign policy.

According to a NBC News online poll of Republican and Republican-leaning voters nationwide, which the network conducted in collaboration with Internet company Survey Monkey, the former neurosurgeon is now backed by 18 percent of GOP supporters and ties with Texas Sen. Ted Cruz. The survey, which was held between Nov. 15 and Nov. 17 among 2,440 Republicans, had a margin of error of plus or minus 2.9 percentage points and showed Trump in the lead with 28 percent.

But a Bloomberg Politics poll released on Thursday still paints the picture of a head-to-head matchup between Trump and Carson, though the former "Apprentice" star once again bested the physician by a margin of 4 percentage points. But most voters noted that they considered Carson more caring, trustworthy and honest in the survey, CNN noted.

Trump, meanwhile, used his Iowa appearance to ridicule Carson for what the mogul called inconsistencies in his life story. He said he found it hard to believe that the doctor continued to impress Iowa voters.

"You have him doing pretty well in the polls - not me," Trump told the crowd.