Story highlights Donald Trump leads in Iowa with 25% support, with Ted Cruz in second at 23%, a Quinnipiac poll shows

Ben Carson, the GOP front-runner there a month ago, is down to 18% and is in third place

Washington (CNN) Ted Cruz has replaced Ben Carson as Donald Trump's chief GOP presidential primary rival in Iowa.

A Quinnipiac University poll released Tuesday shows that Trump is the Republican presidential front-runner in the early voting state, with 25% support among GOP voters likely to participate in Iowa's February 1 caucuses.

But Cruz, the Texas senator, has moved into second place with 23% support -- double the backing he had just four weeks ago. Carson has fallen to third at 18% support, down 10 percentage points from his first-place perch a month ago when he led Trump, 28% to 20%.

Florida Sen. Marco Rubio is in fourth place with 13% support -- the only other candidate in double digits in Tuesday's poll.

Former Florida Gov. Jeb Bush and Kentucky Sen. Rand Paul are tied for fifth place at 5% each and Carly Fiorina at 3%. No other candidate tops 2%.

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