The court appears unwilling to rule that police never need a search warrant when drawing blood, especially when there are other ways to enforce drunk driving laws. NBC's Pete Williams reports.

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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