The two sides differed sharply about the practical consequences of requiring testimony from crime laboratory analysts. Justice Anthony M. Kennedy, writing for the four dissenters, said Philadelphia’s 18 drug analysts will now each be required to testify in more than 69 trials next year, and Cleveland’s six drug analysts in 117 trials each.

Noting that 500 employees of the Federal Bureau of Investigation laboratory in Quantico, Va., conduct more than a million scientific tests each year, Justice Kennedy wrote, “The court’s decision means that before any of those million tests reaches a jury, at least one of the laboratory’s analysts must board a plane, find his or her way to an unfamiliar courthouse and sit there waiting to read aloud notes made months ago.”

Justice Antonin Scalia, writing for the majority, scoffed at those “back-of-the-envelope calculations.”

In any event, he added, the court is not entitled to ignore even an unwise constitutional command for reasons of convenience.

“The confrontation clause may make the prosecution of criminals more burdensome, but that is equally true of the right to trial by jury and the privilege against self-incrimination,” Justice Scalia wrote.

“The sky will not fall after today’s decision,” he added.

The Supreme Court will cut short its summer break in early September to hear a new argument in a momentous case that could transform the way political campaigns are conducted. The case, which arises from a minor political documentary called “Hillary: The Movie,” seemed an oddity when it was first argued in March. Just six months later, it has turned into a juggernaut with the potential to shatter a century-long understanding about the government’s ability to bar corporations from spending money to support political candidates. The case has also deepened a profound split among liberals, dividing those who view government regulation of political speech as an affront to the First Amendment from those who believe that unlimited corporate campaign spending is a threat to democracy.