Ankara is not exactly a model NATO member but the decision to shoot down a Russian bomber in Syrian airspace, as well as its backing of Islamist groups could well be the last straw for the North Atlantic Alliance.

Defense expert Ted Galen Carpenter presented a strong case for considering Turkey's expulsion from NATO in a recent article for the National Interest.

"The reality is that Turkey is an irresponsible loose cannon. NATO is supposed to be an alliance of peaceful democracies. Yet evidence continues to mount that Turkey fails to meet either standard," he noted.

Turkey's "reckless belligerence" as evidence by the Su-24 incident has only been exceeded by the country's "hypocrisy," the expert asserted.

© REUTERS / Reuters TV/Haberturk A combination picture taken from video shows a war plane crashing in flames in a mountainous area in northern Syria after it was shot down by Turkish fighter jets near the Turkish-Syrian border November 24, 2015

Ankara accused Russia of violating Turkish airspace but Turkish warplanes cross into Greece almost daily. In 2014 alone Greek authorities recorded more than 2,000 airspace violations. Turkey's aircraft flew over Greece uninvited 1,306 times in the first eight months of 2015.

"The incident with Russia is worrisome. Fortunately, Vladimir Putin's government has responded thus far only with economic sanctions," the expert stated.

The Su-24 downing is troubling in its own but Turkey's ties with Islamic radicals, including Daesh, also known as ISIL/ISIS, are a major area of concern.

"Turkey, along with Saudi Arabia and Qatar, were major supporters of the Sunni groups that eventually coalesced to form ISIS. Much of the military hardware that ISIS fighters have at their disposal is because of such generosity. … Worse, Turkey has allowed ISIS to ship oil from northern Syria into Turkey for sale on the global market, thus providing a major source of continuing revenue for the terrorist movement," he detailed.

Does NATO really need a "reckless, aggressive ally" like Turkey? Is it willing to provide all the support required by Article 5 of the North Atlantic Treaty if Ankara tries to provoke a major conflict with a nuclear power?

"But it is even worse when that 'ally' shows unmistakable signs of being a fifth column that is aiding and abetting the enemy the alliance has pledged to destroy," Ted Galen Carpenter noted.

The Russian President Vladimir Putin described the Su-24 incident as "a stab in the back" administered by "the accomplices of terrorists." This remark "will badly affect Turkey's reputation in the eyes of the Russians and the Europeans," the Turkish political scientist Aydin Sezer told Sputnik.