The first task of any chief executive is to secure the support of his followers; this is especially true if he's waging a war. That's what George W. Bush did. Six years ago, he went into Iraq to thunderous applause from his conservative Republican base - which stuck with him for years, long after it became clear that he had hyped the rationale for invasion and failed to win the peace.

By contrast, Obama's imminent dispatch of roughly 30,000 new troops to Afghanistan comes at a time when two-thirds of all Democrats are telling pollsters that the war is not worth fighting. The antiwar liberals who propelled Obama's nascent candidacy are worried that an expanded, costly war will wind up sinking his domestic agenda. Democratic strategists are worried that if the war continues to go badly even with the increase in troops (a distinct possibility), liberals might register their disgust by skipping the 2010 congressional elections, thus trimming or imperiling the Democratic majorities on Capitol Hill.

Looming over this week's troop-hike rollout is the specter of Lyndon Johnson. In 1965, when LBJ launched the first major escalation of U.S. involvement in Vietnam, he enjoyed broad national support (that August, only 24 percent of Americans told pollsters that the war was a mistake), and landslide loyalty from congressional Democrats. But by the winter of 1968, his ambitious domestic agenda was in tatters and the party was torn apart from within.

The irony for Obama is that, in the absence of Democratic support, his decision to expand the war will be applauded primarily by the Republicans; nationwide, 60 percent of Republicans are telling pollsters that the war is worth fighting. GOP leaders will probably praise Obama for giving Gen. Stanley McChrystal most of what he wanted, and they'll be glad that Obama has vowed anew to "finish the job," even though nobody really has a clue what a finished job would actually look like.

Lest we forget, however, these people are not Obama's friends. Six months from now, if his benchmarks for success come up short, or if he starts talking about exit strategies (known, in the new parlance, as "off ramps"), they'll quickly morph him into Jimmy Carter and deride him as a wimp incapable of command. Granted, Bush was the president who invaded the wrong country after 9/11 and put Afghanistan on the back burner, thus bequeathing Obama a mess with few cleanup options - but, hey, that's politics.

All the more reason Obama needs support from his own party. Certainly, some Democrats do support the troop increase as essential to our national security. On a Washington blog, a counterterrorism analyst named Jim Arkedis has urged his fellow Democrats to fall in line: "The president will need his party's understanding and support to succeed. If Democrats fall out over Afghanistan, he won't be able to sustain a coherent policy, and the public will likely lose confidence in the party's ability to manage the nation's security."

But that's a very tough sell. The majority Democratic sentiment was best expressed the other day by Michael Cohen, a former State Department speechwriter and current think tank scholar. He sought to rebut Arkedis:

"If you want the public to 'lose confidence' in the Democratic Party's ability to manage the nation's security, then, yes, mindlessly supporting a strategically dubious war in Afghanistan . . . is a jolly good idea. I'm getting ready to watch a Democratic president, to whom I've invested a great deal of emotional energy and support, tragically follow this course. But just because the president makes a decision to send more troops into an Afghan quagmire, it most certainly does not mean that his party should blindly follow course."

And his party won't do that. Congressional Democrats are recoiling at the cost of an escalated conflict - Nancy Pelosi remarked the other day that there is "serious unrest in our caucus about can we afford this war" - particularly in the wake of reports that the price tag per soldier is $1 million a year. They don't want to pay for Afghanistan if it means shelving the party's domestic agenda, so some have suggested a solution: a new tax - or "surcharge" - to help finance the wider war.

A new tax on recession-burdened Americans? To pay for a war that at this point barely musters 50 percent support in the national polls? That's a synonym for political suicide, and thus not likely to happen. But the fact that high-ranking Democrats have even floated the idea is proof of the party's restiveness. (The pro-war Republicans would never support such a move, of course. They preferred to finance Iraq in part by borrowing heavily from China.)

The likeliest money scenario, voiced recently by Joint Chiefs of Staff Chairman Mike Mullen, is that Obama's escalated war will require a supplemental funding bill. Oh, the irony: That's precisely how Bush often did his war business, by circumventing the regular defense budget. During the '08 campaign, Obama won liberal hearts by assailing Bush's budgetary tricks and vowing he'd never finance a war that way. We'll see about that.

Obama is surely trying to chart a pragmatic, nonideological course - signaling that Afghanistan (and, most important, its impact on Pakistan) is a vital security interest, while also stressing that the wider war will not be open-ended. But he will need political strength at home to sustain his daunting mission abroad, and I question whether he can succeed if the liberal base begins to wonder whatever happened to hope and change.