Executive Order 9066
<blockquote>
  <p>In World War II, Executive Order 9066 suspended basic rights of
  Japanese Americans - even people whose loyalty to the United States
  was never questioned, though the government feared the group as a
  whole might contain some spies - and led to a lot of people (>100K)
  being rounded up and kept at internment camps. Korematsu v. United
  States ruled this was constitutional.</p>
  
  <p>Today, in the "War on Terror," at least one politician can make
  surprisingly strong statements about plans for negative treatment
  against large groups of people (e.g. Muslims) because of concerns that
  a small minority of them might be radical enough to kill a bunch of
  people, and [the politician can] remain surprisingly popular.</p>
</blockquote>

<p>What, if any, modern-day obstacles are in place that would nullify the same or materially same executive order?  <a href="https://law.stackexchange.com/questions/5927/could-executive-order-9066-be-repeated-with-other-groups-today">This link indicates: "The Court would then have to adhere to, reconcile with, or overrule Korematsu &amp; Hirabayashi." However, it does not state that there this is the only obstacle and hence the question</a></p>

<p>The main obstacle is that <em>Korematsu</em> is almost universally considered to have been wrongly decided. It is considered "anti-canon". Greene, <a href="http://harvardlawreview.org/2011/12/the-anticanon/" rel="nofollow noreferrer">The Anticanon</a>, 125 Harv. L. Rev. 379 (2011)</p>

<p>Justice Scalia said that the ruling was wrong.</p>

<p>Justice Ginsberg wrote, "A Korematsu-type classification…will never again survive scrutiny." <a href="https://supreme.justia.com/cases/federal/us/515/200/case.html" rel="nofollow noreferrer">Adarand Constructors, Inc. v. Peña</a>, 515 U.S. 200 (1995), (GINSBURG, J., dissenting)</p>

<p>Justice Alito has said, "We have, at times, overreacted in response to perceived characteristics of groups thought to be dangerous to our security or way of life and condemned individuals based on group membership." <a href="https://casetext.com/case/fraise-v-terhune" rel="nofollow noreferrer">Fraise v. Terhune</a>, 283 F.3d 506 (3d Cir. 2002)</p>

<p>Chief Justice Roberts was asked about this during his <a href="http://www.judiciary.senate.gov/imo/media/doc/GPO-CHRG-ROBERTS.pdf" rel="nofollow noreferrer">confirmation hearing</a>:</p>

<blockquote>
  <p>Senator FEINGOLD. [...] Do you believe that Korematsu was wrongly decided?</p>
  
  <p>Judge ROBERTS. It’s one of those cases that I don’t think it’s technically
  been overruled yet, but I think it’s widely recognized as not
  having precedential value. I do think the result in that case—
  Korematsu was actually the—considered the exclusion and not the
  actual detention, but the exclusion of individuals based on their
  ethnic/racial background from vast areas. It’s hard for me to comprehend
  the argument that that would be acceptable these days.</p>
  
  <p>Senator FEINGOLD. It is often included, if you list decisions that
  are sort of considered some of the worst decisions in the history of
  the Supreme Court—</p>
  
  <p>Judge ROBERTS. Yes. </p>
</blockquote>

<p>To a similar question during her confirmation, Justice Sotomayor said, "It is
inconceivable to me today that a decision permitting the detention, arrest of an individual
solely on the basis of their race would be considered appropriate by our government."</p>

<p>Justice Breyer wrote in his book, <em>Making Our Democracy Work</em>, </p>

<blockquote>
  <p>"The decision has been so thoroughly discredited that it is hard to
  conceive of any future court referring to it favorably or relying on
  it."</p>
</blockquote>

<p>During her confirmation hearing, Justice Kagan was asked for examples of cases that were poorly reasoned. She listed only one: <em>Korematsu</em>.</p>

<p>Thus, the main obstacle to such a law is that the judiciary seems to be almost universally convinced that <em>Korematsu</em> was decided incorrectly. However, Justice Scalia cautioned that these sentiments might be put aside again in times of war: </p>

<blockquote>
  <p>"In times of war, the laws fall silent. [...] That’s what happens. It
  was wrong, but I would not be surprised to see it happen again — in
  time of war. It’s no justification but it is the reality."</p>
</blockquote>

<p>An alternative view, somewhat in line with Justice Scalia's outlook, is offered by Justice Jackson in his dissent in <em>Korematsu</em>. He recognizes that the courts might be pressed again to defer to military decision-making ("I would not lead people to rely on this Court for a review that seems to me wholly delusive") and proposes that the chief constraint against this unconstitutional action is the executive's "responsibility to the political judgments of their contemporaries and to the moral judgments of history." I take that to stand for the principle that it is up to the people to make it clear that such an order is unacceptable.</p>

<p>Not many, if any, that weren't in place at the time of EO 9066. The fifth amendment clearly states that no person shall be deprived of life, liberty, or property, without due process of the law. Public opinion, political bias, and a court sympathetic to those biases, are what allowed EO 9066 to be enacted.</p>

constitutional-law