If indeed it is the case, as Prime Minister Benjamin Netanyahu alleges, that Iran is behind the heinous murder of Israeli tourists in Bulgaria (and Iran, and its proxy Lebanese militia, Hezbollah, are the likeliest suspects, given their recent attempts to kill Israelis in half-a-dozen countries across the globe), then we've entered a new phase in the confrontation over Tehran's nuclear ambitions.

Already this month we've seen signs that this matter is moving toward confrontation; these signs include a parade of American officials coming to Israel to assure its leaders that they have the situation in hand, and demanding requesting in a firm manner that Israel take no rash steps against Iranian nuclear sites; and the movement into the Persian Gulf of an enormous fleet of American naval vessels, meant to ensure that the Strait of Hormuz, through which a fifth of the world's oil flows, stays open in the event of an Israeli attack, or an Iranian provocation, or some unforeseen crisis.

Iran has been waging war, rhetorical and actual, against Israel, and Jews, for at least 20 years, and is the prime sponsor of anti-Israel terror attacks, including the most notorious Iran-sponsored attack of all, the one that took place 18 years ago today, in Buenos Aires, in which 85 people were murdered at a Jewish community center. Of course, Israel has responded to the eliminationist anti-Israel program of the Iranian regime by battling Hezbollah, assassinating several of its leaders, assassinating Iranian nuclear scientists, and otherwise sabotaging the nuclear program whenever possible. But in this most recent phase of the confrontation -- the last two years or so, when Israel ramped up its campaign to get Tehran to stop its nuclear program -- Iran has been fairly inactive in the successfully-murdering-Jews department.

This is what may have changed earlier today. Prime Minister Netanyahu will be under extraordinary political pressure to retaliate in some serious way, and he will be under more pressure from himself than ever to deal with a regime he believes seeks the annihilation of six million Jews.  As Amos Harel put it in Haaretz yesterday, the nuclear clock seems to be ticking more quickly than ever, and the "the key question will be whether...Netanyahu can fulfill his ideological and historical commitment to prevent what he describes as a potential second Holocaust."

I doubt Netanyahu will retaliate for the Bulgaria bombing by launching an immediate attack on Iran's nuclear sites. But there is a good chance he will launch attacks on Hezbollah targets and individuals, and possibly certain Iranian targets as well, and this sort of back-and-forth can only escalate tensions further, which could only bring us closer to an Israeli preemptive strike on Iran.

Which, of course, is an enormous challenge for President Obama, who can't seem to convince the Israeli leadership that he will deal with the Iranian nuclear program militarily, if need be. Leon Panetta, the secretary of defense, is traveling to Israel later this month, to meet with Netanyahu and the defense minister, Ehud Barak. He certainly won't be the last American official to visit before November.