Numerous U.S. presidents have tried, and failed, to push Israel closer to a lasting peace with the Palestinian people. And on a more immediately ominous topic, repeated warnings by U.S. presidents have also failed to deter Iran from its relentless pursuit of a nuclear arsenal.

Thus, when President Barack Obama visits Israel for the first time starting Wednesday, though peace with the Palestinians will still be on the agenda, the most pressing concern will be that Iranian threat.

President Obama told Israeli Channel 2 last week that while Iran is “over a year or so away” from obtaining a nuclear weapon, the U.S. will use “all options” needed to thwart that quest. He added that “we don’t want to cut it too close.”

The president also offered this unduly optimistic view of Iranian leaders’ thinking: “They are not yet at the point I think where they’ve made a fundamental decision to get right with the international community, but I do think that they’re recognizing that there’s a severe cost for them to continue on the path that they’re on and that there’s another door open.”

Just don’t expect that upbeat notion to carry much weight with Israeli Prime Minister Benjamin Netanyahu — or with anybody else who’s paid attention to Iran’s actions.

Indeed, Mr. Netanyahu is expected to seek the president’s agreement this week on drawing “red lines” past which Iran’s nuclear advance must not go.

Yes, the Obama administration, like previous U.S. administrations, has repeatedly stressed that it won’t allow Iran to reach its nukes goal.

As Vice President Joe Biden put it early this month: “Big nations can’t bluff. And presidents of the United States cannot and do not bluff. And President Barack Obama is not bluffing. He is not bluffing.”

So what happens if Iran “is not bluffing,” either? What about Iranian President Mahmoud Ahmadinejad’s repeated pledges to “destroy” Israel?

Iran has agreed to more talks next month in Istanbul with world powers, including the U.S., that are urging it to give up on getting nuclear arms. Yet previous rounds of such negotiations have bought Iran more time to move ever closer to devastating weaponry.

And on Sunday, Iran launched a destroyer equipped with guided missiles in the Caspian Sea — its initial deployment of a major warship in the oil-rich region, and another indicator of Iran’s military buildup.

Meanwhile, as if the rising Iranian menace weren’t sufficiently harrowing, Israeli officials are rightly alarmed about the growing possibility of Syrian missiles falling into the hands of the terrorist group Hezbollah.

Under these daunting circumstances, Israeli-Palestinian tensions inevitably must take a back seat on President Obama’s trip.

Again, as the president himself put it:

“We don’t want to cut it too close.”