Back in the 1970s and ’80s, in the wake of post-Watergate reforms, which put a brake on the executive power amassed by Richard M. Nixon, a small group of Republicans — including, most notably, Dick Cheney, who was then President Gerald Ford’s chief of staff and later President George H. W. Bush’s secretary of defense — abandoned traditional conservatives’ suspicion of concentrated government power and began looking for ways to expand presidential prerogatives. As Charlie Savage, a reporter for The Boston Globe, observes in his astute and harrowing new book, “Takeover,” those efforts made some progress during the administrations of Ronald Reagan and the first President Bush, and came to startling fruition under the current administration of George W. Bush and Mr. Cheney, now the vice president.

Indeed, Mr. Savage suggests that after Sept. 11 a “perfect storm of political pressures,” including a compliant, Republican-controlled Congress and a public fearful of further terrorist attacks, enabled an aggressive White House to expand vastly the powers of the executive branch and dangerously tip the constitutional system of checks and balances.

Mr. Savage won a Pulitzer Prize this year for a series of articles he wrote for The Globe about executive power and Mr. Bush’s use of “signing statements,” which the president has attached to dozens of laws enacted by Congress, asserting his authority to disregard certain provisions because they conflicted with his interpretation of the Constitution. With “Takeover” Mr. Savage has expanded those articles into a book that is important reading for anyone interested in how the current administration has amped up presidential power while trying to undermine Congress’s powers of oversight and the independence of the judiciary.

Many aspects of this subject have been examined in newspaper and magazine articles and earlier books, and Mr. Savage leans heavily at times on the work of other reporters as well as his own groundbreaking work for The Globe, owned by The New York Times Company. But this volume is distinguished by his ability to pull together myriad story lines into a succinct, overarching narrative that is energized by his own legal legwork and interviews with key figures like John C. Yoo, a former deputy assistant attorney general, and Brent Scowcroft, who was national security adviser to the first President Bush.