WASHINGTON — Sen. John McCain may not travel here again until this summer, but he still may shake up Capitol Hill this spring.

The 81-year-old Arizona senator, who has been battling brain cancer for nine months, is set to release his latest memoir in late May, and is promising a “his no-holds-barred opinions on the current developments coming out of Washington” in the book, according to publisher Simon & Schuster.

“In his forty years in politics McCain has never been afraid to buck trends or ruffle a few feathers,” the company said in a statement this week. “His words are more important today than ever.”

McCain’s latest book (he has already written six others, most focused on his military service and patriotism of other notable leaders) will focus on the 2008 presidential election, where he was the unsuccessful Republican nominee, and the years since.

Inhofe: McCain ‘calling the shots’ away from Washington Sen. Jim Inhofe may be the one running the Senate Armed Services Committee's hearings and answering reporters’ questions. But he insists Chairman John McCain is still in charge.

That will include his tumultuous relationship with President Donald Trump, who famously on the campaign trail mocked McCain’s status as a prisoner of war in Vietnam and has sparred with him on a series of Senate legislative issues.

McCain, arguably the top Republican military policy voice in Congress, will also cover in the new book “vital challenges from abroad: Russia, NATO, the campaign to defeat ISIS, our ongoing operations in Iraq and Afghanistan.”

The announcement comes as Senate lawmakers are starting their spring push on the defense authorization bill, the largest defense policy legislation Congress handles each year.

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As chairman of the Senate Armed Services Committee, McCain is typically the most visible figure in his chamber on that work, grilling a series of high-profile military officials over budget requests and personnel priorities.

Sen. John McCain, R-Ariz., leaves a closed-door session where Republican senators met on the GOP effort to overhaul the tax code on Dec. 1, 2017. McCain has been at home in Arizona since later that month as he recovers from the side effects from his brain cancer treatment. (J. Scott Applewhite/AP)

But the ailing senator has not been on Capitol Hill since early December, when he traveled back home for chemotherapy and recovery. Staff has said that he maintains an active role in planning for the defense policy hearings, and the committee’s second-ranking Republican — Oklahoma Sen. Jim Inhofe — has repeatedly said that McCain is still in charge of all important committee decisions.

In an interview with a local Arizona radio station, McCain’s daughter Meghan said she was “cautiously optimistic” that McCain could return to Washington, D.C. by early summer.

The new memoir — titled “The Restless Wave” — will be co-authored by Mark Salter, a former staffer who also helped him write the books “Thirteen Soldiers” and “Faith of My Fathers.”