Secretary of State John Kerry, then chairman of the Senate Foreign Relations Committee, speaks at a December 2009 hearing. Photo: U.S. Navy Petty Officer 1st Class Chad J. McNeeley.

Witness the transformation of John Kerry from global diplomat to global supplicant, Diplomat-in-Chief to Beggar-in-Chief.

Just a few weeks ago the new US Secretary of State bestrode the world like a colossus. The man who could not be president in 2004 got a new lease of life as second only to the President on the global stage.

And boy was he impressive. That is, until he wasn’t.

First he showed phenomenal moral fortitude in pushing for a strike against Bashar Assad after he gassed hundreds of children.

But then, after making an ill-informed comment about Syria doing a chemical dismantling deal, he quickly relented. Russia came to Assad’s rescue and the butcher of Baghdad has, to date, never been punished for the mass slaughter of kids.

Then Kerry rose to the occasion on Iran, warning the world of the dangers of the mullah’s nukes.

But here we are, just a few weeks later, and Kerry has been reduced to threats of violence against Israel in order to persuade a reluctant world to support his appeasement of Tehran.

Just this morning Kerry warned (threatened?) on MSNBC that failing to reach a nuclear deal with Iran will mean that Iran will get nuclear weapons.

Have we heard this script before?

Last week there was the even juicier nugget that if Israel did not reach an accord with the Palestinians there would be a third intifada, a comment that America’s outstanding Ambassador to Israel, Dan Schapiro, seemed to repudiate in his address to the Jewish General Assembly in Jerusalem.

I’ve discovered as a parent that when I reduced to threats of punishment against my kids it’s really because I have lost the voice of moral authority. Otherwise, I would not need external inducements to persuade them.

I feel bad for John Kerry. He is looking increasingly desperate and ridiculous. He did not learn from his predecessor, Hilary Clinton, who transformed her public image utterly as America’s top diplomat, that strength earns respect.

No, Kerry has gone in the opposite direction.

When he first started as Secretary of State there was the promise that his moral determination to hold tyrannies accountable for atrocities against their people would make America forget some of the things he unfairly said against America’s troops during Vietnam, accusing them of being the troops of Genghis Khan.

I for one could not have been more inspired by Kerry when he sounded the trumpet throughout the world that Assad was a murderer who would have to be punished. I praised him wherever I could. This is exactly what we need. An American foreign policy with a moral center.

Now I see a man whom even the French feel is weak in his negotiations with Iran, and who has been reduced to Twitter battles with Iran’s foreign minister.

What a sad waste of talent.

Rabbi Shmuley Boteach, whom The Washington Post call “the most famous Rabbi in America,” will shortly publish “Kosher Lust: Love is Not the Answer.” Follow him on Twitter @RabbiShmuley.