By Hunter Schwarz

Sen. Jeff Flake has a political target on his back.

The Arizona Republican has been critical of President Donald Trump while promoting his recent book, and Trump is returning the favor. On Thursday, he tweeted Flake was “WEAK on border, crime and a non-factor in the Senate. He’s toxic!”

Trump also praised Flake’s primary contender, Kelli Ward, an Arizona doctor, and will actually travel to Arizona next week to hold a campaign-style rally there, an incredibly aggressive move for a President against a member of his own party.

Flake’s book, “Conscience of a Conservative: A Rejection of Destructive Politics and a Return to Principle,” borrows its title from another book by a Republican senator from Arizona — perhaps one of the most famous books in modern conservatism — Barry Goldwater’s “The Conscience of a Conservative,” published in 1960. I read both to compare, and find out why Flake picked the title.

First, a disclosure: I grew up in Flake’s district when he was a member of the House and interned at his Mesa, Arizona, office one summer. It mostly involved answering the phone and taking notes on the issues constituents called about (yes, they really do track that).

Second, some background: Goldwater ran for president in 1964 and lost to Lyndon Johnson in a landslide, winning only six states (that was the election with the infamous “Daisy” ad, and Goldwater’s “In your heart, you know he’s right” slogan, which was countered by critics with “In your guts, you know he’s nuts”).

Still, he’s often credited as a founder of the modern-day conservative movement, focused on small government and low taxes, and for paving the way for Ronald Reagan. There’s a terminal named after him at Phoenix Sky Harbor airport. Jeff Flake not only holds his seat in the Senate, but he’s the former executive director of the Goldwater Institute, a think tank. Goldwater’s legacy still looms over Arizona and the politicians who represent it.

Flake writes that both books came at a time of crisis for conservatives. Goldwater wrote his “in response to what he saw as an emergency — the collapse of conservative principles, which in his view had been hopelessly compromised by the New Deal.” And he wrote his “because we as conservatives — and conservatism itself — are in crisis” in a time when “gamesmanship replaced statesmanship” and Republicans “stopped speaking the language of freedom and started speaking the language of power.”

Goldwater hit Republicans of his day for campaigning on decreasing federal spending while doing the opposite, and Flake hits Republicans today for behaving in ways they would have protested had Democrats done it (“Conduct that would have had conservatives up in arms had it been exhibited by our political opponents now had us dumbstruck,” he writes of Trump’s praise for dictators and denial of US intelligence agencies’ findings).

Both books were written while a Republican was president — Goldwater’s under Eisenhower — but there’s a noticeable difference in how they handle their party’s control of the White House.

Goldwater mentions Eisenhower on the first page of chapter one, writing that he was concerned by Eisenhower’s comment that he was economically conservative “but liberal when it comes to human problems.” But Eisenhower feels largely absent in the rest of the book. Goldwater spends far more time targeting midcentury conservative enemies like labor unions, a large, tax-hungry, out-of-touch federal government and, in the longest chapter of the book, the Soviet Union.

Flake, however, unloads on Trump, chapter after chapter. Conservatism has been “compromised by a decidedly unconservative stew of celebrity and authoritarianism,” he writes, and he traces the likely birth of “alternative facts” to the “birther” movement, which Trump for years championed. Of the 2016 campaign he writes, “Never has a party so quickly or easily abandoned its core principles as my party did.”

Flake praises and quotes Goldwater throughout his book — a rare moment of disagreement is Goldwater’s opposition to the Civil Rights At of 1964 — and he writes that the title is “an homage to both his fierce independence and his visionary leadership.”

Leaning on Goldwater and his conservative credentials feels in part like Flake’s attempt at inoculating himself from a Republican primary challenger and the Twitter fury of Trump. Sure, I’m attacking a Republican president, it signals, but it’s because he’s not really conservative, and I am. His book is a point of no return that, depending on how his primary goes, could either be blamed for costing him his job or praised as an act of bravery.

There’s a quote that ends both the first and last chapter of Flake’s book reads like justification for doing his own “Conscience of a Conservative.” Each comes after he compares the struggles conservatism faced under Goldwater to the struggle it faces today.

“This is not an act of apostasy,” he writes. “This is an act of fidelity.”