Poll is a welcome sign for Trump, whose rivals are catching up in other early-voting states.
Trump leads Carson by only 1 point in a Fox News national poll.
A new PPP survey shows Clinton with 42 percent support nationally.
The rising poll numbers come after a strong performance in Wednesday's debate.
Retired neurosurgeon Ben Carson follows Trump in second place in the Grand Canyon State.
Trump's net favorables are up 16 percentage points in the last two weeks; Bush is down 6.
Another poll found Sanders pulling within 7 points of Clinton.
His lead over the Republican primary field is growing.
Forty-five percent said they consider her use of a private email server a "serious scandal."
Forty-nine percent of all voters also believe Trump will be the nominee.