On Sunday, an F-18 fighter jet (almost certainly from the Mediterranean-deployed USS George H.W. Bush carrier strike group), downed a Syrian Air Force Su-22 fighter jet.

It was the right decision for both tactical and strategic reasons.

For a start, the Syrian jet was bombing United States allies (the Kurdish-dominated Syrian Democratic Forces) on the ground. It was warned, but did not retreat.

Yet it's not just relevant who the Syrians were bombing, it's also important where they were doing so. Because the Su-22 was striking targets in north-central Syria, proximate to the Islamic State capital, Raqqa, and a town and dam, Taqba.

That locale matters for two reasons.

First, because the Syrian axis (Bashar Assad, Russia, Iran, the Lebanese Hezbollah, and other associated Shiite militias) are determined to displace U.S./allied forces from that area. The Assad axis recognizes that if it secures Taqba, it can push east of the Euphrates river and degrade anti-regime forces operating there with U.S. protection. As I've explained, this area of northern Syria is crucial for the future of the Syrian civil war.

Second, had the U.S. allowed axis forces to displace Kurdish forces from the area, the axis would have been able to disrupt the operation to retake Raqqa from the Islamic State. While the axis argue that they support the U.S.-led effort to defeat the Islamic State, the reality is different.

After all, the axis have vested interests in allowing the Islamic State to survive in some form. While the Islamic State is indeed their enemy, its existence allows the axis to pretend that the choice in Syria is between Assad, and the Islamic State and al Qaeda. Russia, especially, uses this narrative to delegitimate and attack more-moderate U.S.-supported Syrian rebel groups. Ever notice that the Russians always claim they are bombing "terrorists" in Syria? The Islamic State gives them that excuse.

Absent the threat of the Islamic State, the axis powers know that the world would view the Syrian regime much more harshly. Absent international jihadist groups in Syria, the regime would no longer be able to claim "we're the best of a bad bunch."

Still, there's a broader issue at stake here.

This latest axis push against U.S. interests is just the tip of the iceberg. As I noted recently, the axis is also threatening a major U.S. base in south-eastern Syria. Collectively, these efforts are designed to test the Trump administration's commitment to U.S. interests in Syria. Put simply, by escalating their threat against the U.S., and by dangling the prospect of future U.S. casualties, the Assad axis wishes for the Trump administration to back away from its resistance to Assad's regime. They believe that, as was the case with President Barack Obama's red lines, the U.S. can ultimately be compelled to yield.

For that reason, the U.S. response on Sunday was the right one.

A two-person U.S. aircrew in an advanced multirole fighter met a Soviet-era aircraft and outmatched it.

The United States remains the world's sole superpower. Realistic in our appraisal of national interests and prudent in their pursuit, our adversaries must never doubt our resolve.