FEW CABINET positions are more important than secretary of the treasury. President-elect Donald Trump’s choice for the job, Steven Mnuchin, is a smart financier who knows his way around a balance sheet.

That much was evident during Mr. Mnuchin’s confirmation hearing before the Senate Finance Committee on Thursday. Under aggressive questioning by Democrats, Mr. Mnuchin defended his takeover of the failing IndyMac bank at the height of the 2008 panic: Housing advocacy groups have said he and his partners made a killing by turning the institution into a “foreclosure machine.” While acknowledging the mistakes and excesses that sometimes cost borrowers their homes, Mr. Mnuchin reminded the committee that his group took over IndyMac’s distressed loan portfolio in response to the federal government’s search for private investors to bail it out so as to limit taxpayer losses.

He was less successful in explaining his belated disclosure of more than $100 million in assets until the eve of the hearing, or in explaining how the Trump tax cuts would not blow a large hole in federal finances; instead, he invoked the Trump team’s boosterish forecasts for economic growth as an elixir for deficits. On at least one important point, however, Mr. Mnuchin followed the encouraging example of previous Trump Cabinet nominees who have disagreed at their hearings with the president-elect’s more dubious policies or attitudes. Specifically, Mr. Mnuchin said that trade policy is not about limiting imports, it’s about growing exports, an implicit but obvious contrast to Mr. Trump’s blaming of China’s perfidy for the trade deficit and threats to slap tariffs on car imports from Mexico.

Most refreshingly, Mr. Mnuchin was willing to dispute Republican orthodoxy regarding the Internal Revenue Service, the perennial whipping boy of the GOP. The IRS, which resides within the Treasury Department, has lost 17 percent of its budget in real terms since 2010, along with 23 percent of its enforcement staff, thanks in part to reflexive hostility to the tax-collection agency from the GOP in Congress. Mr. Mnuchin told the committee that he is “very concerned” about the lack of staff and up-to-date technology at the IRS. Modernizing the IRS would be “one of my great priorities,” Mr. Mnuchin said. Acknowledging that cutbacks have been counterproductive to the public interest, in that they make it harder for the hard-pressed IRS staff to collect all the taxes due the government, he assured the committee that “the president-elect understands the concept of where we add people, we make money.”

Sen. Mike Crapo (R-Idaho) asked Mr. Mnuchin to guarantee that the IRS would never use its powers to target individuals because of their political views. This was an allusion to the “scandal,” hyped by Republicans, about supposed IRS harassment of conservative groups. But the point could apply equally well to the next p resident, who would be in a position to abuse the IRS’s power to quash legitimate political opposition. “You have my 100 percent assurance,” Mr. Mnuchin replied, thus accepting a key limitation on executive power, and a standard to which every administration must be held.