Justices indicated Wednesday that the dangers of drunken driving don't trump the Fourth Amendment, peppering lawyers for the state of Missouri with objections to their request that the Supreme Court allow law enforcement to order blood tests for DUI without suspects' consent.

The case, Missouri v. McNeely, is seen as a landmark that could clear up almost 50 years of uncertainty over the constitutionality of blood tests that are conducted without a warrant. Legal scholars say it could rewrite drunken-driving laws in all 50 states.

The case hinges on how you interpret a 1966 opinion by then-Justice William Brennan, who wrote (.pdf) that law enforcement should get a warrant before taking a blood draw without a suspect's consent, except in a few very limited circumstances that rise to the level of an emergency.

Missouri wants the court to declare that the dissipation of alcohol in the bloodstream is, on its face, an emergency allowing officers to get a blood test immediately and without a warrant.

But justices indicated that they firmly believed that taking someone's blood was an intrusion that in most cases constituted a government "seizure" subject to protection of the Fourth Amendment and requiring the subject's permission or prior approval from a judge.

"How can it be reasonable to forgo the Fourth Amendment in a procedure as intrusive as a needle going into someone's body?" Justice Sonia Sotomayor asked John Koester, a prosecutor in Jackson, Mo., who represented the state Wednesday.

Related: Full preliminary transcript of Wednesday's arguments (.pdf)

Sotomayor said that if the court ruled Missouri's way, it would be giving law enforcement free rein to "use the most intrusive way you can to prove your case," which wouldn't always be the most constitutionally sound way.

The officer who arrested Tyler McNeely acknowledged that he didn't seek a warrant when he told a hospital lab technician to draw McNeely's blood after a DUI stop in 2010 because he believed he didn't need to, not because he didn't think he couldn't get one in time. 

That troubled several justices, who wanted know how a suspect's fundamental Fourth Amendment rights could be overshadowed for the convenience of law enforcement.

"Why should the Fourth Amendment permit the search to take place without the warrant when it could have been obtained?" Justice Samuel Alito asked Nicole Saharsky of the U.S. solicitor general's office, who joined Koester in arguing Missouri's side.

Justice Ruth Bader Ginsburg said, "It was and I think still is the main rule that if you can get a warrant, you must do that."

Even Antonin Scalia, the court's most law-and-order justice, questioned Missouri's argument, telling Koester, "Once we say that you don't need a warrant, you know, even if things improve, the game's up, right?"

"Why don't you force him (McNeely) to take the Breathalyzer test, instead of forcing him to have a needle shoved in his arm?" Scalia asked.

Justices' questions during arguments don't always signal how they will vote; the justices often pose hypotheticals designed to crystallize or clarify a contrary position.

But Lyle Denniston, a Supreme Court expert writing on Scotusblog, said it seemed clear that "the court is not going to let police across the nation order — on their own authority — the taking of blood samples from those suspected of drunk driving."

"Two impressions were dominant throughout the argument: the Justices generally do regard the use of a needle to take a blood sample as quite an intrusive gesture by the government, and the Fourth Amendment warrant requirement should not be cast aside for all cases of drunk driving when officers decide to order a blood draw," he wrote.

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The U.S. Supreme Court will hear arguments Wednesday in a landmark Fourth Amendment case that could clear up almost 50 years of uncertainty over the constitutionality of blood tests that are taken without a suspect's consent.

The case involves a traffic stop in Missouri, but its ramifications could range far wider, potentially rewriting drunk-driving laws in all 50 states.

"It comes down, basically, to are you going to see blood draws every single time someone gets pulled over for a DUI," said Michael A. Correll, a litigator with the international law firm Alston & Bird, who examined the legality of blood draws in the West Virginia Law Review last year. 

Because drunk-driving stops are such an everyday occurrence, "it's going to affect a broad area of society," he told NBC News, adding: "This may be the most widespread Fourth Amendment situation that you and I are going to face" for the foreseeable future.

Writing last month in the journal of the Texas District and County Attorneys Association, Lauren Owens, a research attorney for the organization, said, "The outcome of the case could lead to a dramatic increase in the number of DWI cases supported by blood evidence."

The case began in October 2010, when Tyler McNeely of Cape Girardeau, Mo., about 100 miles south of St. Louis, was pulled over for speeding. According to court documents, McNeely was unsteady and failed field sobriety tests, so state Highway Patrol Cpl. Mark Winder asked him to take a breath test.

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When McNeely refused, Winder took him to a hospital, where McNeely refused to take a blood test. Winder told the lab technician to take a sample anyway. The record shows that at no time did Winder seek a warrant compelling the test, which indicated that McNeely's blood-alcohol level was almost double the legal limit.

But McNeely's lawyers persuaded the trial judge to exclude the evidence as a warrantless search in violation of the Fourth Amendment to the U.S. Constitution:

The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.

Here's where it gets complicated. Earlier in 2010, the Missouri Legislature changed the state's "implied consent" law, which says that if you drive on Missouri's roads, you've automatically consented to take a sobriety test. 

The previous language said explicitly that if you refused to take a test, then "none shall be given" and the refusal itself could be used as evidence against you.

The new language left out the four words "none shall be given," re-emphasizing that the driver had consented simply by having gotten behind the wheel in the first place. Winder testified that he had read a journal article about the change and said he made a "conscious decision" not to seek a warrant "due to the law changes."

On appeal, the state argued that no warrant was needed because of a 1966 U.S. Supreme Court ruling in a California DUI case that laid out circumstances under which law enforcement could order a blood test without a warrant.

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In general, a person's blood is protected under the Fourth Amendment, Justice William Brennan wrote in Schmerber v. California (.pdf): "Search warrants are ordinarily required for searches of dwellings, and, absent an emergency, no less could be required where intrusions into the human body are concerned."

But Brennan noted that Armando Schmerber, the driver in the California case, had been in an accident. Because the officer had to investigate the scene and make sure Schmerber was taken to a hospital for treatment, "there was no time to seek out a magistrate and secure a warrant" before the driver's body metabolized the alcohol in his system, Brennan wrote.

So Brennan carved out what he called a "stringently limited" exception to the Fourth Amendment's warrant requirement because of the likelihood that evidence — the alcohol in the driver's blood — would be destroyed during the delay. That clause has come to be known as the "exigent circumstances" or "special facts" exception. 

Missouri argued that delaying McNeely's blood test while the officer sought a warrant amounted to an exigent circumstance because the alcohol in his blood would be destroyed. McNeely argued that because his case involved a straightforward DUI stop — he wasn't in an accident, unlike Schmerber in 1966 — Winder had plenty of time to seek a warrant.

Missouri's Supreme Court agreed with McNeely in January 2012, writing (.pdf):

The patrolman here, however, was not faced with the "special facts" of Schmerber. Because there was no accident to investigate and there was no need to arrange for the medical treatment of any occupants, there was no delay that would threaten the destruction of evidence before a warrant could be obtained. ... The sole special fact present in this case, that blood-alcohol levels dissipate after drinking ceases, is not a per se exigency pursuant to Schmerber justifying an officer to order a blood test without obtaining a warrant from a neutral judge.  

As the court itself noted, Brennan stressed 47 years ago that his analysis was expressly limited to the facts of the Schmerber case, but that hasn't stopped various state and federal courts from referring to it over the years, not all of them reading it the same way. 

So in May, the state of Missouri asked the U.S. Supreme Court (.pdf) to step in because "this emerging conflict on a fundamental Fourth Amendment issue will likely continue to divide courts throughout the United States."

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The federal government has sided with Missouri, writing in a friend-of-the-court brief (.pdf) that "the fact that the evidence of intoxication is necessarily leaving the suspect's system provides the required exigency." Prosecutors from across the country joined to file a similar brief (.pdf).

But the American Civil Liberties Union, which is representing McNeely, argued that there were no special circumstances trumping the Fourth Amendment.

In any event, it told the Supreme Court (.pdf), the issue is groundless, because — as he testified himself — the arresting officer ordered the blood test because he thought he could, not because of any "special facts." That means it's "a strange case in which to construe the exigency exception to the Fourth Amendment," the ACLU argued.

The court's decision is likely to come down to one simple question, Correll said: "Did Schmerber create a blanket exception to the Fourth Amendment or didn't it?"

"What does the court indicate the emergency is?" he asked. "Is the emergency the inability to get a warrant in a set period of time, or is the emergency that the blood alcohol is dissipating?"

As for McNeely, he's not off the hook even if he wins. Under a separate law that isn't at issue, his driver's license was revoked because he refused to take the breath and blood tests. And both sides agree that the blood test wasn't the only evidence against him, meaning he could still be convicted of felony drunk driving.

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