The rising clamor over the beheading of two Americans, and rapidly sinking polls, forced President Obama to reassure the nation last week he had a plan to deal with the Islamic State. He did some of what he had to do, but only some, and so most military analysts believe the expanded airstrikes will not be a sufficient match for the size and weaponry of the terrorist army.

They miss the point. The disjointed speech wasn’t really about terrorism and launching a new war. It was about saving Obama’s presidency.

He is sinking fast and could soon pass the point of no return. In fact, it may already be too late to save the SS Obama.

The whole second term has been a string of disasters, with the toxic brew of his ObamaCare lies, middling economic growth and violent global breakdown casting doubt on the president’s stewardship. Six years into his tenure, nothing is going as promised.

Earlier on, he could have trotted out his teleprompters and turned public opinion his way, or at least stopped the damage. But the magic of his rhetoric is long gone, and not just because the public has tuned him out.

They’ve tuned him out because they’ve made up their minds about him. They no longer trust him and don’t think he’s a good leader.

Most ominously, they feel less safe now than they did when he took office. Americans know the war on terror isn’t over, no matter what their president claims.

Those findings turned up in a tsunami of recent polls that amount to a public vote of no confidence. They shook up the White House so much that the plan to grant amnesty to millions of illegal immigrants was put on hold to try to protect Democratic candidates from voter wrath in November.

That was a necessary tactical retreat, but it doesn’t change the ­basic calculation. The president’s problem is that he has been wrong about virtually every major issue.

His worldview, his politics, his prejudices, his habits — they’ve been a mismatch for the country and its needs. He has been a dud even in the one area where he seemed a lock to make things better, racial relations. Only 10 percent believe race relations have improved under him, while 35 percent said they are worse, according to a New York Times survey. The remainder said there wasn’t much change either way.

That’s shocking — but not surprising. Barack Obama was not ready to be president, and still isn’t. It is a fantasy to believe he’ll master the art in his final two years.

The lasting image will be his yukking it up on the golf course minutes after giving a perfunctory speech on the beheading of James Foley. It revealed him as hollow, both to America and the world, and there is no way to un-see the emptiness.

That means, I fear, we are on the cusp of tragedy. It is reasonable to assume the worst-case scenarios about national security are growing increasingly likely to occur.

Obama’s fecklessness is so unique that our adversaries and enemies surely realize they will never face a weaker president. They must assume the next commander-in-chief will take a more muscular approach to America’s interests and be more determined to forge alliances than the estranged man who occupies the Oval Office now.

So Vladimir Putin, Iran, China, the Islamic State, al Qaeda and any number of other despots and terrorists know they have two years to make their moves and advance their interests, and that resistance will be token, if there is any at all.

Throw in the fact that Europe largely has scrapped its military might to pay for its welfare states, and the entire West is a diminished, confused opponent, ripe for the taking. Redrawn maps and expanded spheres of influence could last for generations.

Of course, there is a possibility that America could rally around the president in a crisis, and there would be many voices demanding just that. But a national consensus requires a president who is able to tap into a reservoir of good will and have his leadership trusted.

That’s not the president we have.

Cuomo forced to turn and fight

News flash: Politicians are people, too. They change direction when they feel pain.

Take Andrew Cuomo. His promise to join general-election debates marks a change of behavior. Pain made him do it.

Cuomo avoided talking to primary rival Zephyr Teachout, and voters punished him. The turnout was under 10 percent, of which he got 62 percent, meaning he won the nomination with the backing of just 6 percent of those eligible to vote.

Landslide? No! He won but emerged weaker, which explains why the governor says he will debate Republican Rob Astorino. He even promises “debates” — plural.

The promise comes with an asterisk. Unclear is whether Cuomo will agree to one-on-one showdowns with Astorino, or insist on a Noah’s Ark of minor-party candidates.

He’ll do the minimum he thinks he can get away with. That’s where pain comes in, again.

If you want real, substantive debates about the critical issues facing the Empire State, tell him. Until it hurts.

Democrats’ praise for ‘the enemy’

Shhhh, don’t tell Chuck Schumer and Harry Reid, but New York Democrats are saying nice things about David Koch.

Reps. Carolyn Maloney and Jerry Nadler and a sprinkling of city and state lawmakers joined Koch to praise him for funding the renovation of the plaza in front of the Metropolitan Museum of Art.

As Maloney made clear, she was endorsing Koch’s philanthropy, not his conservative politics. “This beautiful addition to the Met Museum exists because of one man’s generosity,” she said.

The gift brings to about $1.3 billion what Koch has given to charities, including Lincoln Center, the American Museum of Natural History and medical institutions New York-Presbyterian, Memorial Sloan Kettering and the Hospital for Special Surgery.

Yet Senate Democrats, led by Reid and Schumer, have called Koch and his brother Charles un-American and accused them of trying to buy elections. The Koches’ great sin is to spend some of their money opposing the Democratic agenda.

Reid, supported by Schumer, even tried to silence them and curb their First Amendment rights by giving government more power to limit political speech. Fortunately, the effort failed.

As for the Dems who showed up to praise Koch, it shouldn’t be noteworthy when pols put New York ahead of their party. But it is, and that’s the real disgrace.

Islamophobic? Try anti-Semitic

Liberals love to seize on any perceived anti-Muslim bias to claim New York suffers from severe Islamophobia, but official statistics show that Jews suffer far more attacks.

The Post reports that anti-Semitic incidents jumped 35 percent so far this year, with 85 incidents compared to 63 last year. The number of anti-Muslim hate crimes was 15, compared to seven last year.

Some things never change.