The Fourth Amendment prohibits the police from searching individuals without a warrant, but the Supreme Court allows exceptions to that rule for “exigent circumstances” — when the police believe that the delay involved in getting a warrant would lead to destruction of evidence.

In Missouri v. McNeely, scheduled for argument at the court on Wednesday, the police forced a driver to take a blood test at a hospital without a warrant, after he refused to take a breath test with a portable machine when he was stopped for erratic driving. The blood test showed that his blood alcohol content was 0.154 percent, or almost twice the state’s legal limit.

The Missouri Supreme Court wisely ruled that the warrantless blood test was an unreasonable search because there was no emergency that prevented the police from getting a search warrant in a timely manner before the alcohol in the driver’s blood dissipated.

Missouri is now asking the United States Supreme Court to overturn the state court ruling and to radically revise Fourth Amendment law so that police — without a warrant — can draw blood from every person arrested on suspicion of drunken driving, regardless of the circumstances. The United States government, siding with Missouri, argues that warrantless blood draws are needed “to prevent the imminent destruction of evidence.”