"Facts matter." That's what Vice President Joe Biden said during the portion of last night's debate with Congressman Paul Ryan that related to Iran. Facts especially matter when discussing what the debate's moderator called the biggest national security threat facing the United States. So, how were Vice President Biden and Congressman Ryan on the facts about Iran's nuclear program and the sanctions aimed at ending this program?

Vice President Biden rhetorically asked "…how close the Iranians are to getting a nuclear weapon," and concluded "They are a good way away." Congressman Ryan appeared to agree with this politically favorable timeline, arguing "We can debate the timeline, whether there's -- it's that short a time or longer. I agree that it's probably longer."

It is convenient to say there is still time to prevent Iran from obtaining nuclear weapons. There is. But how much? Iran's current stockpile of enriched uranium would be sufficient to fuel several nuclear weapons, if it were enriched to weapon-grade and converted from gas to metal. As of the last International Atomic Energy Agency report, Iran had over five tons of uranium enriched to about 3.5 percent U-235, and about 100 kg of uranium enriched to 20 percent U-235. U-235 is the fissile form of uranium needed to fuel a nuclear weapon.

Iran's growing stockpile of 20 percent material brings it much closer to nuclear weapon fuel: enrichment to this level accomplishes 90 percent of the work necessary to bring natural uranium to weapon-grade. But even its stockpile of low-enriched uranium is a large step in the right direction, as it accomplishes about 70 percent of the work necessary to bring natural uranium to weapon-grade. In either case, further enrichment to weapon-grade would take a matter of weeks or months, depending on the number of centrifuges devoted to the task.

But how is Iran doing on making a device that could cause the weapon-grade uranium to explode in a nuclear chain reaction - a process called weaponization? According to the International Atomic Energy Agency, Iran appears to have had a structured weaponization program through 2003 and a less structured one since then. However, making the weapon-grade fuel is the most difficult step in a nuclear weapon program: it is about 90 percent of the work. Indeed, it's normally assumed that no country would produce weapon-ready fuel unless the rest of the components of the bomb were finished and waiting.

Congressman Ryan: "When Barack Obama was elected they had enough fissile material, nuclear material, to make one bomb. Now they have enough for five."

This statement is misleading because Iran does not currently have nuclear weapon-ready material to fuel even one nuclear weapon. When President Obama took office in January 2009, Iran had nearly enough U-235, within its low-enriched uranium stockpile, to fuel one nuclear weapon. Iran now has enough U-235 in this stockpile to fuel about five nuclear weapons. However, this U-235 isotope must be separated from the more abundant U-238 isotope through enrichment. The finished product should contain over 90 percent U-235. Iran could use the thousands of centrifuges it has installed at the Natanz enrichment plant to do the job, or the smaller plant at Fordow, but both are visited regularly by international inspectors. Or Iran could use a secret plant. In any case, it is a necessary step for Iran on the path to nuclear weaponry.

Vice President Biden: "What Bibi held up there was when they get to the point where they can enrich uranium enough to put into a weapon, they don't have a weapon to put it into."

Not quite. During his speech before the U.N. General Assembly, Israeli Prime Minister Benjamin Netanyahu argued that producing enriched uranium fuel for a nuclear weapon - not the weapons package itself - is Iran's main challenge. Iran has been working at uranium enrichment for years and is close to achieving its goal, according to Netanyahu. Iran should have enough uranium enriched to 20 percent U-235 to fuel a weapon "by next spring, at most by next summer." At that point, Netanyahu said, "it's only a few months, possibly a few weeks" before Iran can produce enough enriched uranium for a first bomb, and the remaining nuclear weapon components could be produced in "maybe under a year, maybe only a few months."

Iran has had access to an implosion bomb design and there is strong evidence, presented by the International Atomic Energy agency, that Iran has undertaken activities "relevant to the development of a nuclear explosive device." The only plausible purpose for many of these activities is to make nuclear weapons. Activities described by the Agency include high explosives testing simulating a nuclear explosion, studies and experiments with an initiation system used in nuclear detonation, the development of specialized detonators used in nuclear weapons, and work on making and shaping high-enriched uranium metal components.

Vice President Biden: "Both the Israelis and we know we'll know if they [the Iranians] start the process of building a weapon."

That might not be as easy as it sounds. Almost all weaponization work is laboratory scale, which is not easy to detect. An example is the Iraqi site of Al Atheer, a key nuclear weapon laboratory under Saddam Hussein's regime. This site was unknown to U.S. intelligence and so was not bombed by the United States during the first Gulf War in the early 1990s. Following the war, international inspectors discovered it to be Iraq's major facility for developing nuclear weapon components.

Congressman Ryan: "We've had four different sanctions at the U.N. on Iran, three from the Bush administration, one here. And the only reason we got it is because Russia watered it down […]"

This suggests that the Bush administration muscled through three tough sanctions resolutions at the United Nations, and that the Obama administration caved to Russia on a fourth resolution. The truth is that all four U.N. Security Council resolutions were watered down in order to buy Russian and Chinese support. Both these countries could have used their veto power to prevent a tougher resolution from being adopted. The logic since December 2006, the time of the first U.N. resolution, has been consistent: some international sanctions are better than none at all. And some resolutions have contained non-binding language about the danger of furthering Iranian proliferation by doing business with Iran's energy, financial, and transport sectors. A number of countries have used this language to impose sanctions that are far stricter than required by the resolutions.

Congressman Ryan: "In Congress, I've been fighting for these sanctions since 2009. The administration was blocking us every step of the way."

The executive branch is typically reluctant to support bills that require it to act in ways that might restrict its diplomatic freedom and compromise relations with other countries. This was as true of the Bush administration as it is of the Obama administration. Congress has - since well before President Obama arrived in 2009 - pushed for tougher sanctions on foreign entities that continue to do business with Iran, including with Iran's energy and financial sectors. Several key bills were signed into law by President Obama in the past two years, including Comprehensive Iran Sanctions, Accountability, and Divestment Act (CISADA) in 2010, and most recently the Iran Threat Reduction and Syria Human Rights Act of 2012.

Congressman Ryan argued that the Obama administration has undermined some of the tougher measures in these new laws by granting waivers to countries considered to have significantly reduced crude oil imports from Iran. He fails to note that half of these countries are in Europe, which has banned the purchase, transport, financing, and insurance of Iranian oil and petroleum products.