We can all agree that this Fourth of July holiday is not particularly festive, given the grim tidings on all fronts. But perhaps the unhappiest Americans these days are the antiwar liberal Democrats who voted with enthusiasm for Barack Obama, only to find him tethered to a protracted war in a remote region that for two millennia has foiled virtually every foreign invader. Even Alexander the Great had to flee with an arrow in his leg.

If George W. Bush were still in office and presiding over the same circumstances in Afghanistan - with Western allies such as Canada pulling out their troops; with U.S. casualties on the rise; with resilient insurgents bedeviling our forces; with a U.S. nation-building effort held hostage by a corrupt host government that lacks grassroots credibility; with a fungible withdrawal deadline; with the prospect of untold billions of dollars being poured into an open-ended occupation - you can bet that liberals would be vocally apoplectic.

But with Obama on the hot seat, they're stuck. Even though Obama is basically trapped in this unwinnable war, even though he's using Bushspeak to talk about all the "progress" we've supposedly made in Afghanistan, liberals don't want to make his political life more miserable than it already is. So mostly they fume about their powerlessness.

Occasionally they do voice their concerns, while recognizing that their efforts are all in vain. Last Thursday night, 153 House Democrats voted for a losing amendment that would have required Obama to set a deadline for the withdrawal of all troops; in the words of one liberal congressman, New York's Jerrold Nadler, "Every dollar we spend in Afghanistan, every life we waste there, is a waste. An intelligent policy is not to try to remake the country that nobody since Genghis Khan has managed to conquer. . . . What arrogance gives us the right to assume that we can succeed where the Moguls, the British, and the Soviets have failed?"

And a few left-leaning journals have entered the fray. What's most noteworthy about the now-famous Rolling Stone article is not its depiction of Gen. Stanley McChrystal's trash-talkers, but, rather, its diligent exposé of a war going badly - as acknowledged by McChrystal's own people. As a top McChrystal adviser said (in a quote that the Obama White House didn't try to refute), "If Americans pulled back and started paying attention to this war, it would become even less popular."

But, for the most part, fervent liberal criticism of Obama has been sporadic or muted. Liberals recognize that they don't have the numbers. In Washington - indeed, as evidenced by the House's decision on Thursday night to OK the next round of war funding - Obama's war is broadly supported by the Republican lawmakers (who actually don't think he's hawkish enough) and by moderate and conservative Democrats who don't want the voters back home to think that they're "soft" on terrorism or disrespectful to the troops.

Actually, liberals have been relatively quiescent for a slew of reasons. For starters, they have the same war fatigue that afflicts most other Americans. Afghanistan (now officially the longest war in U.S. history) and Iraq are simply a drag to contemplate; it's easier to just tune them out, to not even patronize the outpouring of movies that depict the pain. And it's more fun to debate who should be dancing with the stars than whether we should be launching a spring or autumn offensive in Kandahar.

Liberals have been seething about Obama's flexible promise to begin troop withdrawals in July 2011 - the president won't say whether the pace will be fast or slow, and last weekend he mocked those who have an "obsession" with the timetable - but, truth be told, they haven't made a coherent case for a smart alternative policy. That's probably because there are so few alternatives. What happens if we leave Afghanistan on our timetable, and the terrorists now hunkered down in Pakistan take the opportunity to set up shop all over again? Liberals are lamenting what they call "open-ended war," but how do they propose to close Afghanistan to the bad guys?

The bottom line is that they're locked into this war, just like Obama. For most of the past decade, and especially when Bush was fixated on Iraq, the liberal complaint was that America was rushing to avenge 9/11 by invading the wrong country. Liberals, eager to demonstrate that they, too, believed in the application of military force, saw Afghanistan as the right place for a just war - a chance not merely to defeat al-Qaeda on the battlefield, but to bring humanitarian aid to people (especially the women) who suffered human-rights abuses at the hands of the Taliban.

Indeed, candidate Obama was quite clear about his plans for a wider war in Afghanistan. For instance, during a CBS interview in July 2008, he said: "I think one of the biggest mistakes we've made strategically after 9/11 was to fail to finish the job [in Afghanistan], focus our attention there. We got distracted by Iraq." He said, with respect to Afghanistan: "For at least a year now, I have called for two additional brigades, perhaps three" - in other words, as many as 15,000 new soldiers. And that autumn, during his first debate with John McCain, he said: "We have seen Afghanistan worsen, deteriorate. We need more troops there. We need more resources there."

Did liberals not hear what he was saying? Maybe they figured that he had to say those things about Afghanistan to ensure that he wasn't perceived as a Democratic softy; having invested in his campaign, liberals may have seen his stance as nothing more than shrewd politics. Mostly, I suspect that when he attacked the Iraq war and got hawkish about Afghanistan, what liberals actually heard in their heads was simply this: "I'm not a dummy like George W. Bush."

Nevertheless, a wider war in Afghanistan was a key feature of the "change" that liberals voted for, even if they chose not to see it at the time. The immediate political danger for Obama, however, is that the left's unhappy quietude might further depress Democratic turnout in the November midterm elections. With apologies to Alexander the Great, this dearth of enthusiasm could be the next arrow in the president's leg.

E-mail Dick Polman at dpolman@phillynews.com.