The Fourth Amendment generally requires police to obtain a warrant for a blood draw. But in a 5-4 vote on Thursday, the court upheld a Wisconsin law that says people driving on a public road have impliedly consented to having their blood drawn if police suspect them of driving under the influence. It also said that “exigent circumstances” permit police to obtain a blood sample without a warrant.

Justices Samuel Alito, Clarence Thomas, Stephen Breyer and Brett Kavanaugh joined Chief Justice John Roberts in the majority vote.

The liberal leaning Breyer was obviously the swing vote.

While this is a huge victory for police, it’s a setback for 4th Amendment rights advocates.

In his concurring opinion, Thomas wrote that because the evidence of alcohol in drivers’ blood will dissipate over time, states can invoke the “exigent-circumstances doctrine” on that basis alone to allow police to order a blood test without a warrant. Explaining why he took a stand apart from Alito’s plurality opinion, Thomas wrote that it “adopts a rule more likely to confuse than clarify.”

Alito’s concurring opinion agreed that speed is vital in obtaining blood-alcohol evidence. But he also said that the demands on police officers’ time contribute to creating exigent circumstances that allow an exception to warrant requirements — especially if an unconscious motorist has caused a crash. And he noted that police usually take such drivers to the emergency room — removing their chance of administering a breath test at the police station.

Previous cases over similar issues involving the 4th Amendment focused on the privacy of the person and the invasive quality of the blood draw.   After all, what can be more invasive than that?

Twenty-eight states have laws similar to Wisconsin’s. The case, Mitchell v. Wisconsin, was accepted by the court at the start of this year, amid sharp divisions among state appellate courts over whether the blood draws violate motorists’ Fourth Amendment rights.