At first blush, it sounds totally nuts: Why should someone on a suspected-terrorist watch list be able to walk into a gun shop, go through a background check and walk out 20 minutes later equipped with an assault weapon, high-capacity magazines and thousands of rounds of ammunition, ready to inflict the kind of carnage that we saw in Orlando? Given what's going on in the world, why do we act as if we're helpless to prevent such a thing?

Sensing political opportunity, Senate Democrats intend to press that argument hard in floor debate later today. The problem is that on this one, they're wrong.

They're wrong because the courts have held that individuals have a constitutional right to possess firearms for self-protection. And as Republicans accurately point out, in this country, you can't strip someone of a constitutional right by simply placing him or her on some bureaucratic watch list. You have to show good cause for that decision; you have to give the person in question the right to challenge the stripping of their constitutional right in the courts, and the burden of proof in such cases would be overwhelmingly on the government, not the citizen.

Furthermore, someone who is merely on a "watch list" is by definition someone who has done nothing that would allow authorities to arrest that person and charge him or her with a crime, and thus nothing that could justify stripping them of their rights. They are on that list because someone somewhere fears what they MIGHT do someday, and what someone MIGHT do someday cannot be grounds for denying their rights today. It is impossible to write a law that addresses that fundamental problem while still denying "watch list" suspects their right to bear arms.

On other proposed legislation, however, Republicans are on much weaker ground. For example, there is no constitutional or common-sense argument against a proposed amendment requiring background checks before the private sale of weapons through the Internet or at gun shows. Licensed gun dealers have had to use the National Instant Check System for decades now, and allowing private sellers to evade such checks simply encourages a dangerous, untraceable black market in firearms. It's a stupid loophole that could easily be closed if not for the NRA's automatic, absolutist rejection of any form of regulation as a dire threat to the Second Amendment.

And while a ban on the sale of assault weapons such as that used to kill or wound more than 100 people in Orlando is not among the amendments up for consideration before the Senate today, it ought to be. There is no legitimate reason for such weapons to be manufactured or sold in this country.

We've all heard the gun lobby's response to such statements, including its rejection of the label "assault weapons." Fine. "Weapons of mass murder" would do just as well, because that's what they are designed to be. They are not hunting weapons, and they are rarely if ever used in home or personal defense, in large part because other weapons are better suited for such purposes. They are military in design and function, even in their semi-automatic mode, and the military aspect of such weapons is precisely why they are so appealing to certain buyers.

In fact, gun extremists argue that the military aspect of "weapons of mass murder" is precisely why they must remain legal, so that angry citizens have the firepower needed to engage in armed rebellion against the government. No federal court has ever come close to validating that ridiculous theory, and no responsible political party would do so either.

The NRA and its supporters argue that an assault weapons ban would be unconstitutional because the Second Amendment prohibits bans against an entire class of weapons. That too is nonsense. For more than 80 years, federal law has severely restricted the purchase and possession of fully automatic weapons, and since 1939 the NRA and other groups have never mounted a major legal challenge to that law.  There is no reason that semi-automatic "weapons of mass murder" with high-capacity magazines could not be banned as well under that theory.

In Heller v. D.C., the landmark 2008 Supreme Court decision on guns, Justice Antonin Scalia explicitly stated that the Second Amendment applies only to some forms of weapons but not to others. In addition, seven states and a number of localities have long-standing bans against the sale of assault weapons, and every attempt by the gun lobby to overturn those laws on constitutional grounds has been rejected.

The most recent example came just this morning, when the U.S. Supreme Court refused to even hear a challenge to Connecticut's assault-weapons ban, passed in the wake of the Sandy Hook elementary school shooting.

Its vote was unanimous.