WASHINGTON — When President Trump nominated William P. Barr as attorney general a year ago, establishment Republicans who had chafed at Mr. Trump’s takeover of their party were relieved. Between Mr. Barr’s work in the Reagan White House and his fast-track career under George Bush, he could be a bridge to the Republican Party they knew — and preferred.

How wrong they were.

Mr. Barr has eagerly embraced the most divisive and disputed aspects of the Trump agenda, much to the delight of the party’s hard-line conservatives who see him as an indispensable ally in their fight to push the country further to the right on issues like religious liberty, immigration and policing.

Other conservative attorneys general shared Mr. Barr’s relish for political battle. But as he attacks the Democratic Party, assails liberal culture and defends the president against accusations of abusing his office, Mr. Barr has wielded a maximalist view of executive power and adopted a blithely antagonistic, no-apologies style that set him apart from his predecessors.

That makes him a natural fit in a Republican Party that Mr. Trump has remade in his mold. But it worries critics in both parties who fear that Mr. Barr is eroding the Justice Department’s traditional independence in law enforcement. They point to his handling of the Mueller report, which he summarized in a letter widely seen as more favorable to Mr. Trump, and his appointment of a prosecutor to re-examine the opening of the Russia investigation, which Mr. Trump has long impugned.