A new poll shows Clinton with 55 percent support to Sanders's 33 percent.
Carson is tops in favorability: 84 percent of Iowa Republicans view him positively.
A new PPP survey shows Clinton with 42 percent support nationally.
Retired neurosurgeon Ben Carson follows Trump in second place in the Grand Canyon State.
Another poll found Sanders pulling within 7 points of Clinton.
A poll finds Trump would siphon significant support from Bush in a three-way race with Clinton.
Huckabee, Rubio and Paul perform best in head-to-head match-ups with Clinton.
The survey found many years of Washington experience has become a liability for candidates.
Several candidates are in a statistical dead heat, according to CNN's poll.
Democratic firm's poll gives Christie 45 percent support among registered voters.
It's the second national poll in as many weeks to have Carson in the top spot.
Poll is a welcome sign for Trump, whose rivals are catching up in other early-voting states.
The rising poll numbers come after a strong performance in Wednesday's debate.
Trump's net favorables are up 16 percentage points in the last two weeks; Bush is down 6.
Walker, who led for months, is on the decline, with Carson surging to second.
Trump was the preferred GOP presidential nominee for 15 percent of respondents.
Some of us may tune out 2016 campaign coverage before President Obama's second term is half over.
Ohio Gov. John Kasich (R) is closing the favorability gap in the latest polling.
Ryan trails Clinton by 9 percent, while all other potential candidates lag by double digits.