Throughout the 20-month Syrian bloodbath, Team Obama has been telling us that they’ve been playing it low-key because they feared the crisis might spread beyond Syrian borders if we took a bigger role.

Sigh.

Even with a US-supported, Arab League-sponsored Syrian opposition meeting in Qatar this week, the lack of a hard-hitting US reaction to the slaughter (now around 35,000 deaths) yielded exactly what the administration feared most: a region grown even more unstable than before the Syrian civil war.

For instance, news reports wrote last weekend that a couple of Syrian tanks had made their way into the Golan Heights demilitarized zone, raising concerns in Israel about new troubles along that relatively quiet border.

Plus, US ally Turkey and Syria have now exchanged artillery fire several times along their border — not to mention that some believe Damascus has unleashed Syrian Kurdish groups for possible strikes inside Turkey.

Of course, a serious Syrian-Turkish dustup could draw NATO into a fray, since Ankara is a member; NATO has reportedly drawn up war plans for that contingency. The Syrian mess has also affected Jordan’s security. Refugee camps are reportedly filled with bad actors; Jordanian extremists go to Syria to get terror training, intending to return home, according to some press accounts.

In late October, Amman’s security services foiled a major al Qaeda-linked attack. The plotters meant to bomb shopping malls and target Western diplomats, possibly even Americans. The weapons and explosives were reportedly smuggled in from Syria.

The Syrian storm is whipping up trouble in Iraq — pushing the Baghdad government increasingly into Tehran’s orbit and re-radicalizing those who have beefs with Baghdad.

Iraq is turning a blind eye to — if not facilitating — Iran’s arms shipments across the country to Syria. Meanwhile, al Qaeda, which by some estimates has doubled in number in Iraq since US forces left in 2011, is on the march there and in Syria, too.

Indeed, Director of National Intelligence Jim Clapper told Congress earlier this year that some of the violence in Syria had “all the earmarks of an al Qaeda-like attack,” concluding, “We believe that al Qaeda in Iraq is extending its reach into Syria.”

Al Qaeda is using the Syrian war to sharpen its terrorist tradecraft. Its presence there will increase the conflict’s intensity and lethality as well as provide turf for training and operations elsewhere in the region — and, perhaps, beyond.

There’s more: In late October, a massive blast in Beirut killed Lebanon’s pro-West intelligence chief; Syrian security forces are suspected. Street unrest over the Syria question in Lebanon is common.

And Lebanon’s Hezbollah is getting into the act, too. The terror group is working closely (again) with Iran’s Revolutionary Guard to prop up the Assad regime in Syria.

Iran has admitted that its elite Quds Force is in Syria, helping its ally. This is driving Arab states (Saudi Arabia, Qatar, etc.) to distraction with fresh worries over Tehran’s increasingly assertive role in the region.

In sum, it’d be hard to say the conflict hasn’t moved beyond Syria as Team Obama hoped. Shock waves of violence and instability are thundering across the region.

Worse, a continued US policy of self-deterrence on this critical issue will lead to more misperceptions, miscalculation and violence both within and without Syria, involving an untold number of nations and victims as the now-regional crisis unfolds.

Team Obama’s notion that Syria’s troubles wouldn’t spill over was an expedient and convenient excuse for not exercising American leadership. And we’re only just beginning to see the real cost of that decision.

Peter Brookes is a Heritage Foundation senior fellow and a former deputy assistant secretary of defense.