A strange thing happened the other day in Washington, D.C.: Marco Rubio actually showed up for work.

These days, a Rubio sighting in the Capitol is rare, the birdwatcher’s equivalent of spotting a blue-footed booby. Like all senators who’ve run for president, Marco’s been away a lot.

The reason for his recent detour to Washington was to cast a very important vote affecting the security of this country, and of all the Floridians he’s supposed to represent.

The Senate was considering a law to prevent persons on the FBI’s terror watch list from buying explosives or guns. To most Americans, that’s a no-brainer.

Rubio showed up to vote against the bill. This was only one day after the mass shootings in San Bernardino.

The measure was defeated by the Republican majority, slaves as always to the NRA, which opposed the law. (Rubio isn’t the only GOP senator running for president who’s terrified of the gun lobby. Rand Paul, Ted Cruz and Lindsey Graham voted against the watch list ban, too.)

In his prime-time speech from the Oval Office, President Barack Obama asked: “What could possibly be the argument for allowing a terrorist suspect to buy a semiautomatic weapon?”

Political cowards can always find an argument. Rubio and others, including Jeb Bush, say they’re concerned about the accuracy of the government’s no-fly list, which is a part of the FBI’s consolidated watch list.

The no-fly database was initiated after 9/11 to stop terrorists from boarding commercial airline flights. In its early years, the list included some improbable names, including Sen. Ted Kennedy, the deceased 9/11 hijackers and hundreds of others that shouldn’t have been there.

We don’t know exactly who’s on the no-fly list now, because it’s secret.

Rubio says banning gun sales to everybody that the FBI considers a possible threat would penalize innocent citizens who are mistakenly put on the list. He got this script straight from the NRA.

The real bad guys on the watch list must be laughing their butts off. We won’t let them get on an airplane, but they can stroll into any gun shop and buy an AR-15.

According to the General Accounting Office, more than 2,000 persons on the U.S. terror watch list were able to legally purchase firearms between 2004 and 2014. If that doesn’t scare you, nothing will.

Since 2007, the government has pushed Congress to prohibit the sale of weapons and explosives to those on the terror watch list. As president, even George W. Bush supported such a ban.

Over and over it gets defeated, led by NRA stooges like Rubio. (He also voted against a bill to have gun-show dealers and online firearms sellers use background checks to identify convicted felons and mentally ill persons).

U.S. intelligence gathering is far from flawless, as we know from 9/11. But what’s the point of making lists of potentially dangerous individuals if law enforcement can’t act on that information to avert future bloodbaths? It’s likely that some of those 2,000-plus persons on the watch list who have bought weapons pose no harm to the public. It’s also likely that some have violence in mind, and these plots can simmer for years.

If the day ever comes when one of those watch-list suspects uses that legally purchased weapon for mass murder, part of the blame will fall on those in Washington who made it so easy.

Just try to find Marco then.