Sen. Jeff Flake, a moderate Republican seeking re-election next year, has written a book detailing his brand of conservatism and how it relates to rifts in the Republican Party, according to a report Tuesday.

The New York Times says Flake, R-Ariz., is kicking off his re-election campaign with the rollout of his book, which he wrote without telling his political advisers.

Flake, a fiscal conservative with an independent streak who is a vocal proponent of immigration reform, is facing pressure from the Left and Right as he bids to retain his Senate seat.

Allies of President Trump aim to punish Flake and may help draw a conservative primary opponent against him for his outspoken rejection of Trump, the Times report said. Flake never endorsed Trump in the campaign and called for him to withdraw from the race after the release of the "Access Hollywood" tape. Flake has continued to oppose Trump as president, speaking out against his trade policies and his decision to rein in former President Barack Obama's Cuba policy.

The Times says only in recent days has Flake begun to inform allies about his book.