That mistake has given Russia and Iran a chance to inordinately increase their influence in Syria and in the region. The administration’s failure to gain useful intelligence early on, working to learn more about the opposition and assist in its efforts, has further set back any U.S. effort to hasten Assad’s removal.

Obama’s mishandling of Syria and failure to act more decisively earlier has made a complex problem even tougher now. Like our involvement in Libya, an earlier and more assertive action plan could have strengthened the opposition movement at a more opportune juncture and earned us the trust of the Syrian people, as we eventually (though belatedly) did in Libya.

But is it too late for the United States to do anything about Syria now? Absolutely not.

Although the U.S. position that Assad must go has been the right one, this demand has not been coupled with action. The Obama administration needs to stop hoping for the U.N. and other countries to resolve this on their own. American leadership is needed. The U.S. should mobilize our allies and, together, make clear to Assad that using chemical weapons is unacceptable and will have devastating consequences for him and his regime.

We can still work with our allies to establish safe zones. We can still provide valuable aid to the Syrian opposition forces in the form of food, medicine, communications equipment, intelligence and logistical support. We should still assign Robert Ford, our former ambassador in Syria, as the envoy to the Syrian opposition, encouraging him to engage Jordan and Turkey and to lay the groundwork for a relationship with a post-Assad Syrian government.

Even this late in the game, we still have a chance to get Syria right. The U.S. must step up to the plate now and act in our best national security interest. If not, President Obama will forever live with the consequences — a blundered policy, America’s weakened standing and a prolonged humanitarian crisis.

Marco Rubio, a Republican, is a U.S. senator from Florida and a member of the Senate’s Intelligence and Foreign Relations committees.