Arizona Sen. Jeff Flake says President Donald Trump is not unfit for office, despite Flake’s harsh criticism of the president in his new book as an “unpredictable” and “volatile” commander-in-chief given to “flying off the handle.”

Flake also defends his “yes” vote on the so-called “skinny repeal” of Obamacare, a bill that was voted on three hours after it was first introduced, with no hearings or debate. Many Republicans didn’t like the bill and were hoping the House would kill it.

Yet Flake cast the “yes” vote while making a plea in his book for a return to regular order - hearings, amendments and full debate of legislation before a vote.

Flake was my newsmaker guest on this weekend’s “Sunday Square Off” to discuss his book, “Conscience of a Conservative," a brutal indictment of his own party and president, and a desperate call for a return to conservative values.

The book’s withering critique of Trump and a Republican Party that’s “lost its way” create new challenges for Flake in what appears to be an uphill struggle to win a second Senate term next year.

Flake defends vote for ‘skinny repeal’

A new Arizona poll-- done last week as the book was being released but right after Flake cast several votes for repealing Obamacare-- shows Flake has huge unfavorability ratings with voters as a whole and the Republican base in particular.

The Public Policy Polling survey shows just 18 percent of Arizona voters approve of the job he's doing, while 62 percent disapprove.

More troubling for Flake, the president he scorches in his book is vastly more popular than the senator among the Republican base.

Arizona Republicans approve of President Trump's performance, 65 percent to 30 percent - a net favorability of 35 points. They disapprove of Flake’s performance, 57 percent to 22 percent - a net unfavorability of negative 35.

Trump’s allies have discussed funding a Flake opponent in next year’s GOP primary, but haven’t settled on a candidate.

Former State Sen. Kelli Ward of Lake Havasu City, who was defeated by Sen. John McCain in last year’s Senate primary, is Flake’s only declared primary opponent.

Also on this weekend’s “Square Off,” a "Left/Right" debate between Catherine Alonzo, chief executive officer of the Democrat-leaning consulting firm Javelina, and Chris Baker, a Republican political consultant at Blue Point.

Up for debate:

-Are Jeff Flake's terrible polling numbers for real?

-Should former Sheriff Joe Arpaio get jail time after being found guilty of criminal contempt?

-Will you get to vote on blocking Arizona’s school-voucher expansion? The campaign against the expansion faces a Tuesday deadline for turning in signatures to get on the ballot in November 2018.

-Why did Sen. John McCain ignore Gov. Doug Ducey when McCain voted down the Senate’s Obamacare repeal?

“Sunday Square Off” airs at 8 a.m. Sundays on 12 News, after “Meet the Press.”