Last August, President Obama declared that the Syrian regime's use of chemical weapons was a "red line." About four months later, Al Jazeera released unconfirmed reports that a gas attack killed seven civilians in a rebel-held neighborhood of Homs. Last April, the UK, France, and Israel each claimed that there was evidence that the Syrian government had used chemical weapons in Aleppo, Homs, and/or Damascus. By April 25th, the U.S intelligence assessment was that the Assad regime had likely used sarin gas, but President Obama dodged his red line by announcing that a thorough investigation was still needed (as if the Syrian government would ever allow one). Meanwhile, reports from foreign intelligence agencies and journalists continued to corroborate the use of chemical weapons by the Assad regime. So why did Obama's requirement of a thorough investigation to confirm the crossing of his red line suddenly vanish last Friday?

Viewed through the lens of domestic politics, Obama's Syria epiphany looks conveniently timed to deflect attention from an ever-swelling wave of scandals: Benghazi-gate, IRS-gate, AP/Fox-gate, and now NSA-gate and State Department prostitution-gate. As the film Wag The Dog highlights, international crises are great at diverting attention from domestic scandals.

But from the perspective of the Syrian rebels, the timing and nature of U.S. military assistance may be viewed as either too little, too late, or a cynical attempt to ensure a perpetual stalemate. After all, the outgunned rebels have needed lethal weapons from the U.S. for over two years. Chemical weapons use by the Assad regime is old news. So what has changed? The Syrian regime recently defeated rebel forces at the crucial battle in Qusayr, a town providing a strategic supply conduit for rebel forces in Homs. After the military gains enabled by the robust battlefield support of Iran-backed Hezb'allah, the Syrian regime is now preparing for a major offensive to retake Aleppo. With another crushing blow to a key rebel stronghold, the regime could ultimately prevail in the conflict, unless the U.S. provides just enough rebel support to restore the pre-Qusayr stalemate.

Obama has already made it clear that any lethal weapons or no-fly zone provided by the U.S. would be limited. Such tentative U.S. involvement is unlikely to end the carnage, given the vigorous support that the Assad regime enjoys from Iran, Hezb'allah, and Russia (which could undermine a U.S.-imposed no-fly zone by supplying Syria with its potent S-300 missile defense system). Indeed, the New York Times reported on June 14th that "the president's caution has frayed relations with important American allies in the Middle East that have privately described the White House strategy as feckless. Saudi Arabia and Jordan recently cut the United States out of a new rebel training program, a decision that American officials said came from the belief in Riyadh and Amman that the United States has only a tepid commitment to supporting rebel groups."

What a difference two years makes. In 2011, the relatively non-sectarian Free Syrian Army (FSA) was the main force fighting for freedom from Assad's tyranny. Sunni Islamists had not yet felt compelled by FSA failures to join (and ultimately lead) the military effort in large numbers. In 2011, Obama also had far more credibility and political capital -- important presidential assets when undertaking a foreign military intervention.

But now the Syrian crisis has deteriorated into a regional sectarian war, increasingly creeping over Syrian borders and into Lebanon, Turkey, Iraq, Israel, and Jordan. The Syrian belligerents have also radicalized, decreasing the odds that the ultimate victor will be friendly to the U.S. or able to achieve a postwar reconciliation and reconstruction in Syria.

Today, with a death toll exceeding 90,000 Syrians (and increasing by 5,000/month) and millions displaced, the humanitarian need for intervention is greater than ever. But Iran and Russia are redoubling their support for the Assad regime, so the U.S. must not enter the Syrian cauldron with half-measures or it could suffer a costly setback with far-reaching repercussions. If Obama's "red line" was crossed months ago and the tardy "consequences" are America's feeble and ineffective entry into the Syrian civil war, then Iran, North Korea, China, Russia, and other U.S. adversaries will only feel emboldened to challenge U.S. interests.

Thus, Obama effectively has two choices: 1) continue his disengagement from Syria to preserve whatever political capital and military deterrent he has left for the inevitable showdown over Iranian nukes, 2) enter the Syrian fray in a massive way that ensures a military victory and says to the Iranian regime: "you are next, unless you discontinue your nuclear program." After the U.S. invasion of Iraq in 2003, Iran feared that thousands of American troops would turn eastward and offered to negotiate the dismantling of its nuclear weapons program. The Bush administration refused to engage but Iran still temporarily suspended its nuclear program out of trepidation.

U.S. entry into the Syrian conflict could defeat Assad and deter Iranian nukes, but only with the resolve and overwhelming firepower to demolish the Syrian-Iranian-Hezb'allah axis (ideally with help from NATO forces). Joining the conflict with insufficient commitment mainly to distract a scandal-weary U.S. audience could have catastrophic consequences for the U.S., and that would be the biggest scandal of all.

Noah Beck is the author of The Last Israelis, a doomsday thriller about the Iranian nuclear threat and current geopolitical issues in the Middle East.