WASHINGTON — Deputy Attorney General Rod Rosenstein laid aside the stress of one part of his job Monday to put himself in a different kind of pressure cooker: an argument at the Supreme Court.
Dressed in a traditional morning coat and striped pants, with the added flash of a pair of presidential cufflinks, Rosenstein represented the Trump administration in a case about a prison sentence for a convicted drug dealer at a rare afternoon session of the court.
‘‘Not bad,’’ he said before the arguments, showing the cufflinks briefly to friends who had come to watch him argue. The cufflinks were sent last week by White House counsel Don McGahn, a Justice Department spokeswoman said.
For a little while, Rosenstein was able to cast off the worries of overseeing the investigation into Russian meddling in the 2016 election and the occasional public musings from President Trump about whether to fire him.
The plan for Rosenstein to appear before the justices has been in the works for months.
The solicitor general’s office argues almost every Supreme Court case in which the government is involved. But it will occasionally cede its place to the attorney general or the second in command.
Attorney General Jeff Sessions has not argued a case, nor did the two attorneys general under President Barack Obama: Eric Holder and Loretta Lynch. Previous attorneys general who have argued at the court include Robert F. Kennedy, Janet Reno, and Michael Mukasey.
The justices will have another encounter with the administration Wednesday, when it considers a case on the third and latest version of Trump’s ban on travel from some countries with majority Muslim populations.
Opponents of the policy and some lower courts have labeled it a ‘‘Muslim ban,’’ harking back to Trump’s campaign call to keep Muslims from entering the country.
The high-stakes arguments at the Supreme Court could offer some indication about how a court that runs on respect for traditions and precedent will deal with a president who regularly breaks with convention.
Apart from the campaign statements, Trump’s presidential tweets about the travel ban and last fall’s retweets of inflammatory videos that stoked anti-Islam sentiment all could feature in the court’s discussion of the travel ban’s legality.
Just before the justices returned from lunch Monday, Rosenstein wiped his face with a handkerchief and steeled himself for the court’s inevitable grilling. It was fairly mild, at least compared with the heat he has gotten on social media, including from the president.
Almost halfway through the session, it was Rosenstein’s turn.
‘‘General Rosenstein?’’ Chief Justice John Roberts said, inviting Rosenstein to defend the modified sentence a judge imposed in the case from New Mexico.
At issue was a difference of six months — 9½ years or nine years — between the judge’s sentence and what the defendant wanted. The issue is how much explanation a judge must give when a sentence is modified.
He appeared comfortable answering a steady stream of questions from seven justices over nearly 30 minutes.
Justice Clarence Thomas almost never asks one and didn’t Monday, and Justice Neil Gorsuch is not taking part in the case, probably because he was involved in an earlier phase of the case when he served as an appellate judge.
What if a judge merely checked a box in 600 resentencing proceedings and said no more, Roberts asked.
‘‘In no case is the court merely checking the box,’’ Rosenstein said, challenging the premise of Roberts’s question.
Justice Sonia Sotomayor wondered what should happen if a judge believed that African-Americans should be punished more severely for crimes. The defendant in this case is Hispanic.
‘‘How are we to determine that reason didn’t play a part in this?’’ Sotomayor asked.
‘‘Courts presume that district courts know the law and apply it faithfully,’’ Rosenstein replied.
After the arguments, Rosenstein, his wife and two daughters posed for photos on the front steps of the court beneath the phrase ‘‘Equal Justice Under Law’’ etched into the pediment.
In a separate matter Monday, the Supreme Court has turned down an appeal from a Missouri man who committed robbery and other crimes on a single day when he was 16 and now isn’t eligible for parole until he’s 112 years old.
The justices left in place defendant Bobby Bostic’s 241-year sentence.
Bostic’s defense team had argued that the prison sentence violated the Constitution’s ban on cruel and unusual punishment.