Sen. Joe Lieberman has a bad idea.

The Connecticut senator has proposed that U.S. citizens who serve international terrorist organizations be stripped of their citizenship.
It’s a sad day when Glenn Beck (!) offers a more eloquent defense of constitutional rights than the normally statesmanlike senator from Connecticut.
But let’s leave aside the constitutional formalities and just consider: Would Lieberman’s proposal accomplish anything? The idea behind stripping a terrorist of citizenship is to avoid a morass of litigation over which precise rights the terrorist possesses.
Unfortunately, any attempt to strip terrorists of citizenship will itself plunge prosecutors into an even deeper morass of litigation.
Here’s why:
Congress long ago enacted a version of the law Lieberman is now suggesting. In 1940, Congress passed a new Nationality Act. The act granted the president broad powers to strip citizenship from Americans who showed themselves loyal to a foreign power.
Under the 1940 act, an American could lose citizenship rights not only by enlisting in a foreign army – or accepting office in a foreign government – but even by voting in a foreign election.
The Supreme Court upheld this broad law in 1958, but reconsidered it in 1967.
In that year’s case, Afroyim v. Rusk, Justice Hugo Black wrote:
“The very nature of our free government makes it completely incongruous to have a rule of law under which a group of citizens temporarily in office can deprive another group of citizens of their citizenship. We hold that the Fourteenth Amendment was designed to, and does, protect every citizen of this Nation against a congressional forcible destruction of his citizenship, whatever his creed, color, or race. Our holding does no more than to give to this citizen that which is his own, a constitutional right to remain a citizen in a free country unless he voluntarily relinquishes that citizenship.”
Following the case, Congress amended the nationality law. U.S. citizens can be deprived of their citizenship if – and only if – they have betrayed their allegiance to the United States “with the intention of relinquishing United States nationality.”

Even bearing arms against the United States merely creates a presumption that the citizen intended to relinquish his nationality. The treacherous citizen retains the right to rebut that presumption in court.
Which means that if Lieberman’s law were in effect today, we would not short-circuit any legal process against alleged terrorists like Faisal Shahzad. To the contrary! We’d be on our way to court right now to litigate the issue whether the Times Square bomber’s bombing plot indicated an intent to relinquish his nationality. Only after taking that issue through trial and appeal (maybe multiple appeals) could we get to work questioning and punishing him.
But while Lieberman’s solution is faulty, he identifies a truly serious concern. Why on earth did we allow Faisal Shahzad to become a U.S. citizen in the first place? Before entry – and certainly before naturalization – is the time for scrutiny and exclusion. Afterward is too late.
Shahzad apparently obtained his citizenship through marriage, after an extended sojourn of uncertain legality in this country. Authorities did not discern his radicalism, but even if they had, there was probably nothing they could have done about it: aliens can be excluded if they have a history of violence or if they belong to a list of designated terrorist organizations. But proven sympathy for anti-American radicalism is not grounds to exclude them. 
Even if the law allowed exclusion on those grounds, background checks on immigrants are spotty and unreliable. How could it be otherwise? The U.S. citizenship system is overwhelmed by a flood of applicants and evaders.
Which is one more reminder of why immigration restriction is indispensable to counter-terrorism success, not only in the U.S. but in all the western world.