“How could he do this to businesses as a business guy?” Joe Casey, then a top executive at a Massachusetts bank, Seacoast Financial, recalled asking colleagues whose companies had to pay up after the Romney administration closed a tax loophole. “It was very aggressive, and it was a surprise.”

For the next three years, the Romney administration relentlessly scoured the tax code for more loopholes, extracting hundreds of millions of corporate dollars to help close budget gaps in a state with a struggling economy. It was only after Mr. Romney was gearing up in 2005 for a possible White House bid that he backed away from some of his most assertive tax enforcement proposals amid intensifying complaints from local companies and conservative antitax groups in Washington…

An examination of the period reveals a more complicated picture. It shows a governor who sometimes put the need to find new revenues ahead of the conservative argument that tax increases almost by definition kill jobs; a shrewd financial manager who aides said was guided by a strong sense of rectitude, not just pragmatism; and a political aspirant willing to buck the orthodoxies of his own party — at least, state lawmakers said, until his national ambitions tempered that impulse and led him to steer a more conservative course.

Today Mr. Romney rarely, if ever, discusses on the campaign trail how he closed the Massachusetts tax loopholes.