Our allies need reassurance that we are in the fight for the long haul. After making the case to the American people that we must confront the Islamic State of Iraq and Greater Syria (ISIL), the president chose not to include the buy-in of the American people through their elected officials in the decision to use force.

Last year, the president was singing a different tune. Then, he recognized the importance of seeking authority from Congress for military action after Syrian President Bashar Assad used chemical weapons to kill his own people.

In his address to the nation on Aug. 31, 2013, President Obama said, "Yet, while I believe I have the authority to carry out this military action without specific congressional authorization, I know that the country will be stronger if we take this course, and our actions will be even more effective. We should have this debate, because the issues are too big for business as usual."

After that speech, the Senate Foreign Relations Committee passed an authorization. But instead of grinding through the hard work of securing votes necessary in the House and Senate, Obama abruptly abandoned it.

Instead, he opted for a Russian-brokered deal to eliminate Syria's chemical weapons, and Assad went on murdering his citizens by other means.

Today, more than 200,000 Syrians have been killed and Syria, along with Iraq, has become the headquarters of ISIL, one of the most barbaric and well-financed terrorist groups of our time. This threat should not come as a surprise. For more than three years, the civil war in Syria has raged, creating a perfect environment for ISIL to grow stronger and more sophisticated.

Despite his worthy goal of avoiding unnecessary war, the president bears great responsibility for these developments, particularly for his lack of strategy in Syria and his decision not to keep a residual force in Iraq. The president's long-overdue Middle East policy change is a grudging recognition of that. It is the absence of American involvement, not its presence, that has allowed the problem to fester.

There is no doubt that the president has the authority as commander in chief to respond to immediate threats to the nation, including protecting the country from the threat of a terrorist attack. But conducting a multiyear military campaign against a new enemy in a new country merits its own specific authorization that the president requests and helps move th rough Congress.

Congressional authorization is important for practical and legal reasons. Such a sign of U.S. consensus would help restore our credibility with allies in the region who have questioned the president's resolve after he abandoned plans in Syria to help the moderate opposition.

Last year, I co-authored bipartisan legislation to arm and train the moderate opposition. Rather than support our work, the president ignored it. Now, after hanging the Syrian opposition out to dry and, just last month, claiming that it was a "fantasy" to believe helping Syria's moderates could have made a difference, the president is calling for Congress to provide resources to do just that at a time when its efficacy has become more questionable.

Unless the president reverses course and requests congressional backing, our efforts to confront ISIL risk failure without the long-term domestic political support necessary for a multiyear campaign in at least two countries.

We would be stronger and our actions against ISIL more effective if the president requested authorization. Congress, and the American people, would give him that authority as long as his plan is well thought out. It's the right thing to do for Americans heading into harm's way.

Bob Corker, R-Tennessee, is the ranking Republican on the Senate Foreign Relations Committee.