A Russian fighter jet plummets to the ground after being shot down by the Turkish military on Tuesday. (Haberturk TV Channel/European Pressphoto Agency)

FOLLOWING TURKEY’S shoot-down of a Russian military jet Tuesday, Western leaders rightly addressed themselves to heading off an escalation between Moscow and a NATO member. In the process, they were not as clear as they could have been about where responsibility for the incident lay. So we’ll say it: The first shoot-down by a NATO member of a Russian plane in 60 years is the result of the reckless and increasingly dangerous behavior of Vladi­mir Putin’s regime.

As NATO’s secretary general and a U.S. military spokesman confirmed, the SU-24 plane was struck after crossing into Turkey’s airspace; according to a statement by the Turkish Embassy in Washington, it was one of two planes that violated the frontier. Also confirmed by Western officials is that the Russian pilot failed to respond to 10 warnings.

Moreover, the airspace violation was not an isolated incident. Russian aircraft have repeatedly entered Turkish airspace since beginning operations in Syria in September. Russia apologized for one violation in October; in another case, it denied responsibility for a drone that Turkey shot down. NATO officials said the previous airspace violations looked deliberate — perhaps because they were not limited to Turkey. In the past several years Russian aircraft have invaded the airspace of and submarines have cruised the waters of numerous NATO and European countries — not to mention Mr. Putin’s outright invasion of Ukraine.

Mr. Putin claims Russian forces are in Syria to fight the Islamic State, but there were no jihadist forces in the area where the SU-24s were operating. Instead, they were attacking areas held by militias made up of ethnic Turkmen and backed by Turkey. Just last week the Turkish government summoned the Russian ambassador in Ankara to demand that Moscow stop bombing Turkmen villages, warning that “this could lead to serious consequences.” Russia’s response was to carry out new raids and to violate Turkish airspace.

Mr. Putin no doubt has been calculating that Turkey, like other NATO members, would not dare respond to his provocations with force. When he was proved wrong, like a bully unexpectedly punched, he resorted to lies and slanders: Russian planes were not in Turkish airspace; Turkey was defending the Islamic State; the attack was “a stab in the back.” That last phrase was made famous by another strongman, in Germany in the 1930s. It should give pause to those in the West who still cling to the notion that Mr. Putin can be converted into an ally.