Right after the massacre in Paris, the question on many a pundit's lips was: How will the struggle against Islamic State terrorism affect the 2016 U.S. presidential campaign?
Now, the more pertinent, and worrisome, question is: How will the 2016 campaign affect the struggle against Islamic State terrorism?
To put it more broadly, can the United States actually wage an effective fight against the Islamic State, as many both at home and abroad expect, much less meet broader global responsibilities, when our leaders are obsessed with short-term advantage in domestic politics?
To be sure, Americans have never achieved perfect consensus, even amid the greatest national security crises. Abraham Lincoln faced serious opposition in the 1864 election; Woodrow Wilson battled dissenters during World War I; the Cold War was a time of broad anti-Soviet consensus but also domestic turmoil.
Yet the defining feature of the current American scene is the sheer speed and ferocity with which every issue, even a seemingly indisputable one like the need to respond to the Paris attacks, becomes a source of partisan conflict - and, increasingly, intra-partisan conflict.
For Republicans, the most important fact about Paris seemed not to be the bloodletting itself, but that it contradicted President Barack Obama's claims to have "contained" the Islamic State, or that the president's modest plan to admit vetted Syrian refugees could be recast as a threat to national security and exploited to suit the GOP base's anti-immigration mood.
This is an odd posture for a party that holds a majority in Congress and, therefore, could pass a declaration of war against the Islamic State tomorrow, if it wanted.
For his part, the president indulged in wishful thinking about the threat and, rather than adjust accordingly, vented his frustration with GOP partisanship in defensive and querulous public comments that deflated confidence - and suggested that what really bothers him, in this world of Islamic State-spawned chaos, are the fools he must suffer in Washington.
We have come a long way, in terms of national cohesion, from the Sept. 11, 2001, al-Qaeda terrorist raid, a seemingly galvanizing event that prompted even then-President George W. Bush's Democratic opponents to put the 2000 election dispute behind them, grant Bush wide war-making powers and rally to the flag.
The Iraq war and a global financial crisis undid all of that, ruined Bush politically - and damaged the legitimacy of both U.S. global leadership and U.S. capitalism. Those shocks spawned the furious debates of the Obama years, which have accelerated the ideological and racial sorting of the two parties, leaving them heavily influenced by base voters who, albeit in different ways, question the essential fairness and efficacy of U.S. institutions.
Perhaps Donald Trump will not ride white identity politics all the way to the presidency; Bernie Sanders's socialist "political revolution" may be already fizzling. But these two men and their followers have set the terms of debate in their respective parties, as their rivals' attempts to keep up with them demonstrate.
At a deeper level, this country is still struggling to adapt its contemporary purposes to a federalist constitutional structure whose very design disfavors decisive, centralized state action.
In modern times, Americans have built both a welfare state and a national security state; but the constitutional heritage of limited government assured that these would always be somewhat improvised and hence vulnerable to political attacks ostensibly based on "true" American values.
As Cambridge University historian Gary Gerstle aptly puts it in his new book about the federal establishment's growth, "Liberty and Coercion," the United States in 2015 is ruled by a "government of enormous capacity and influence but insufficient authority."
The months ahead will determine whether American politics can still generate enough consensus to shore up that authority, enabling the United States to lead the fight against the Islamic State - and meet other large challenges.
Already, U.S. squabbling and vacillation have created an opening in global politics for Russia's Vladimir Putin, who offers himself to France as an anti- terrorism ally almost as militarily powerful as the United States but less constrained by democratic politics. This development alone should give us pause, since it is the United States that has an actual legal duty, under the NATO treaty, to aid Europe if asked.
The Islamic State poses a global menace, whose evil purposes - if not, yet, its actual capability - rival those of Hitler's Germany. Unchecked, it would subject much of the world to theocratic dictatorship; massacre and torture "infidels"; enslave women; and, generally, undermine the freedom, prosperity and security that the United States and other modern nations have sacrificed so much to achieve.
Any differences Americans have among ourselves are utterly insignificant compared with our common interest in vanquishing this threat.