Editorial writer and columnist

Since the dawn of the republic, American statesmen have understood that this country cannot isolate itself from world politics but that the U.S. position in the world hinges on taming the factions and partisanship that inevitably plague domestic politics.

In the Federalist No. 11, Alexander Hamilton argued that ratifying the Constitution would create a solid American front against the “arrogant pretensions” of imperial Europe.

“It belongs to us,” Hamilton wrote, “to vindicate the honor of the human race, and to teach that assuming brother” — Europe — “moderation. Union will enable us to do it. Disunion will add another victim to his triumphs.”

Channeling Hamilton 160 years later, Republican Sen. Arthur Vandenberg of Michigan said that partisan politics stops “at the water’s edge” — and rallied the GOP behind treaties and institutions that a Democratic president, Harry S. Truman, fashioned to secure peace and freedom after World War II.

Today, the question before Congress is ostensibly narrow: whether to give President Obama a green light to use military force against the Assad regime in Syria to enforce the international norm against using chemical weapons.

As framed by historical circumstances, though, the issue is far more fateful: What’s left in the fund of national unity upon which the United States has drawn, time and again, to support its global role?

Denied backing from the United Nations, Britain’s parliament and public polls, Obama has turned to a Congress more polarized along partisan lines than any other in recent memory, according to a recent analysis by the Pew Research Center.

There is three times more ideological divergence between the parties than in 1947, when Vandenberg spoke, reflecting growing divisions among the public generally.

In foreign affairs, the organizing principle of Cold War containment is gone; in its place, a long but inconclusive struggle against Middle East terrorism and instability has produced weariness and divisions that cut across partisan lines.

If only Congress were split along neat two-party lines! But it’s splintered among Democratic doves and Republican neocons, Republican libertarians and Democratic humanitarian interventionists.

Obama showed chutzpah tossing the Syria hot potato to this disputatious bunch, since he contributed to this predicament by drawing a “red line” on the use of chemical weapons that Syrian President Bashar al-Assad was bound to cross, and even now he asserts unilateral constitutional authority to strike.

Only a few days ago, Obama, sounding a lot like anti-intervention Republican Sen. Rand Paul, warned against “jumping into stuff that does not turn out well, gets us mired in very difficult situations, can result in us being drawn into very expensive, difficult, costly interventions that actually breed more resentment in the region.”

Having demonized House Republicans who demonized him, and having said he doesn’t need to wait for Congress on various domestic policy issues, Obama invokes constitutional procedure and requests bipartisan aid, even as a White House aide, speaking on the condition of anonymity, offers The Post a crasser view of congressional prerogatives: “We don’t want them to have their cake and eat it, too.”

An interesting question is whether Republicans will demand a price for cooperation, payable in White House concessions on the immigration and budget issues crowding Congress’s fall agenda and about which both the GOP and Obama have jockeyed for political advantage.

For all that, Congress should think long and hard before denying Obama the authority he seeks. This would be true even if Republicans occupied the moral high ground with respect to political polarization — which they do not. It would be true even if Americans were not justifiably war-weary — which they are. And it would be true even if Obama were not sounding such an uncertain trumpet.

Those Republicans, and Democrats, tempted to vote no need to consider the precedent they may be setting and the signal they would send not only to Syria, or Iran, or North Korea — but also to allies from Jordan to Japan.

They should acknowledge the same fact that Obama has at times seemed to deny but that his reluctant call for action in Syria tacitly concedes: The fantasy of a United States “disengaged” from the Middle East, much less from our wider role as guarantor of minimal international order, is just that — a fantasy.

Costly as it is for us to assume global responsibilities, it would be even costlier, in the long run, to abdicate them amid internal political discord, which is why Vandenberg evolved from a pre-World War II isolationist to a postwar internationalist.

The regime in Damascus has already concluded that the United States has been decisively weakened by international isolation and domestic division.

An official newspaper, Al-Thawra, crowed that the mere fact that Obama felt obliged to seek support on the Hill constituted “the start of the historic American retreat.” Will Congress confirm or refute Al-Thawra’s analysis?

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