April is the unforgiving month that will make or break the Obama presidency. It will be a fitting climacteric for a half-term in power that has been an unremitting succession of crises. This month, from Moammar Gadhafi to the U.S. Capitol, Barack Obama will have to master events or see his credibility — and America's — degraded, and his political future — and his party's — imperiled.

In Libya, the president brilliantly passed the first test, securing a multilateral, Arab-sanctioned coalition that took control of the skies above the battleground just in time — and within hours after the improbable passage of a U.N. Security Council resolution. He then endured domestic, often nakedly opportunistic criticism in order to exercise a constructive ambiguity about the mission, professing its genuinely humanitarian purpose while pursuing the harder imperative of national interest, the end of the Gadhafi regime.

Now comes the really hard part. Having intervened, the only acceptable outcome is victory — not the partition of Libya, and surely not the resurgence of a mad dictator who, as the world's attention turned away, would return to the slaughter of his own people. The United States, to invoke a phrase from the past, would look like a "pitiful, helpless giant," with debilitating consequences to our security and the world's. Think of America's standing if Gadhafi defied and defeated this intervention. Think of Obama's standing then — and remember Jimmy Carter's after Desert One, when helicopters sent to rescue our hostages in Iran crashed in the desert outside Tehran.

I wouldn't count on Obama's buckling in Libya or bending to Boehner.

The president, who constantly reads history, certainly doesn't intend to repeat it here. But after the initial successes of the air-covered Libyan rebels, they were suddenly driven into retreat. There are other signals that point in a more hopeful direction. The CIA is on the ground in Libya; the country's foreign minister, a longtime Gadhafi henchman, has defected and fled to London. His decision reflects a cold calculation that the despot he served can't outlast the will and firepower of the U.S. and its allies.

It's for Obama to make that come true, despite the reservations of Turkey and the remonstrance of Russia and China, which wouldn't at all mind American humiliation in the sands of North Africa. NATO, suddenly at least nominally in charge, operates by consensus. This is the price of a useful multilateralism — and the challenge. The president can't let process overwhelm purpose. The United States, Britain, and France have to move the coalition to a consistent application of the airborne equivalent of Colin Powell's doctrine of overwhelming force. Every Gadhafi tank, column or artillery unit should be a target — hit now and again — to end the conflict swiftly. Maybe it can't be stated this explicitly, but the humanitarian mission can't be separated from the strategic goal of removing an inhuman totalitarian who threatens not only his own people, but who would present a constant threat to the region, to Europe, and by aiding and abetting terrorism, to the U.S. as well.

As we've witnessed with Newt Gingrich and John Boehner, rank politics transcends the water's edge. Thus Mike Rogers, the Republican Chairman of the House Intelligence Committee, who doesn't seem very smart about the issue, opposes arming the rebels because we don't know enough about them. But we know all we need to about Gadhafi — and we know how that America's position and influence globally are on the line in Libya. Maybe Rogers is smart in a cynical and unworthy way, willing to see Gadhafi win if that means Obama loses.

But the politics doesn't stop there. Most presidents facing a foreign crisis don't have to contend with a simultaneous domestic threat. Obama does — in the form of a government shutdown or a refusal to raise the debt limit. Either represents another sure path to casting this country as a feckless, helpless giant.

On the budget and the debt limit, the Republicans who control only one house of Congress are compelled more to demanding than actually negotiating, pressured internally to hold America hostage to a know-nothing Tea Party fringe. The leadership realizes this is wrong on the merits — and risky politics.

But the politics will cut the other way unless the president stands his ground here, too. He wasn't elected to preside over the shredding of the social safety net or draconian cuts that would endanger recovery. Boehner may be so afraid of losing his job as speaker to a right-wing coup that he's ready to see hundreds of thousands more Americans without jobs — or the whole nation with degraded schools, depleted Social Security and Medicare, and devastating reductions in health care. That prospect is precisely Obama's opening — and his duty to defend against.

If the GOP spurns real compromise, then the time for ritual invocations of bipartisanship will have passed. The president will have to set and argue the choice — not for the sake of party, but in the name of widely shared, mainstream American values. This is what Bill Clinton did when Newt Gingrich shut down the government in the 1990s. It was a turning point. Now we are at another one. And which direction it turns will depend most of all on the resolve and voice coming from the White House.

Obama, on the campaign trail and in office, has displayed a remarkable combination of patience and then decisiveness. He's won the big ones. But they don't come much bigger than they have this month.

The Republicans have a sad sack of 2012 candidates. Their best hope may be a mayday for this presidency.

But if I were them, I wouldn't count on Obama's buckling in Libya or bending to Boehner. Instead, for this president , for the country, and for progressive principles here and in the world, April could be both the most trying and, in the end, the best of months.