Editor's note: Jeffrey Toobin is a CNN senior legal analyst and a staff writer at The New Yorker. A former assistant U.S. attorney, Toobin is the author of several critically acclaimed best-sellers, including "The Nine: Inside the Secret World of the Supreme Court" and "Too Close to Call: The 36-Day Battle to Decide the 2000 Election."

New York (CNN) -- It was the most vivid, and unexpected, confrontation of Wednesday's State of the Union address.

It happened when President Obama said this: "Last week, the Supreme Court reversed a century of law to open the floodgates for special interests -- including foreign corporations -- to spend without limit in our elections."

In the audience, Justice Samuel Alito, President Bush's second appointee to the Supreme Court, could be seen shaking his head and saying, it appeared, "Not true, not true."

Who's right? As for what the court decided in Citizens United v. FEC, Obama seems to be right -- mostly. In a 5-4 decision, written by Justice Anthony Kennedy and joined by Alito, the court held that corporations, labor unions and other organizations had the right under the First Amendment to spend unlimited amounts of money to influence the outcomes of elections.

If a corporation now wants to saturate the airwaves for or against any candidate for office, including on the eve of the election, it now has the Supreme Court's say-so to do it.

Obama was on shakier ground when he said foreign companies now had the same unlimited rights to participate in our elections. The court's opinion very carefully said it was not deciding the issue with regard to foreign entities. So the court may yet give the green light to these foreign companies -- but it hasn't done so yet.

On the larger question of whether Alito should have expressed himself in this restrained but unmistakable way, I'm with the justice. Attending the State of the Union has always been an awkward duty for the justices -- sitting through these political addresses and wondering when it's appropriate to applaud or react.

Gloves come off after Obama rips ruling

When the president is paying tribute to the armed forces, or making an otherwise uncontroversial point, the justices usually join in the clapping; when the point is more political -- like the one Obama made about Citizens United on Wednesday -- the tradition is for the justices not to react.

But it's wise to remember that the justices are human beings, with strong views on many subjects, including their own decisions. When Obama was criticizing the court's work (as was his right), Alito had the right to react the way anyone would who had taken a shot in a high-profile setting.

In my book, even a Supreme Court justice -- even at the State of the Union -- is entitled to grimace and mutter. (It is worth noting that Alito does seem to have an ax to grind with Obama. As a senator, Obama voted against Alito's confirmation, which the justice does not seem to have forgotten. When the President-elect Obama made a courtesy call on the justices shortly before his inauguration last year, Alito was the only member of the court not to attend.)

Still, it's worth remembering who is likely to have the last word in this confrontation. In his speech, Obama went on to say about the court's opinion, "Well, I don't think American elections should be bankrolled by America's most powerful interests, or worse, by foreign entities. They should be decided by the American people, and that's why I'm urging Democrats and Republicans to pass a bill that helps to right this wrong."

The president and the Congress can try -- but it is the court that will have the last word on evaluating whether any new law is constitutional. And Alito, who is 59 years old with life tenure, will likely be passing on the validity of laws long after Obama has left office.

As Justice Robert Jackson said of the court many years ago, "We are not final because we are infallible, but we are infallible only because we are final."

The opinions expressed in this commentary are solely those of Jeffrey Toobin.