Probably the most serious long-term threat to American security is the possibility that terrorists will acquire an unsecured nuclear weapon. It's therefore terrifying that Republicans are holding up the START Treaty that secures that material:

Let's start with START, the proposed nuclear pact with Russia that Senate Republicans such as Jon Kyl (Ariz.) are attempting to derail, at least until the next Congress. Since the expiration of the previous START treaty last December, there have been no U.S. inspectors in Russia to keep an eye on the country's thousands of nuclear warheads. If the Senate doesn't come up with the 67 votes needed for ratification, says Travis Sharp of the Center for a New American Security, there's a risk Russia will retaliate by removing its logistical support for the U.S. war in Afghanistan, abandoning its cooperation in preventing nuclear proliferation, and thwarting U.S. efforts to keep Iran from gaining nuclear weapons.
But don't take his word for it. Listen to Richard Lugar, top Republican on the Senate Foreign Relations committee and one man who still puts the national interest above political considerations. "We're talking today about the national security of the United States of America," he pleaded on Wednesday. "[T]his treaty must be ratified and be ratified in this session of the Congress.... We're talking about thousands of warheads that are still there, an existential problem for our country. To temporize at this point I think is inexcusable."
Or listen to Bob Gates, the Bush/Obama defense secretary. "The new START treaty has the unanimous support of America's military leadership," he wrote in the Wall Street Journal, calling for a strong bipartisan majority to support the treaty because of "the security it provides to the American people."

What's so hair-pulling about it is that our security apparatus is filled with wildly expensive and/or intrusive measures that bring minimal benefit, but the one security intervention with an enormous cost-benefit ratio may get held up because you need the consent of an intransigent and largely insane party.