President George W. Bush announced Tuesday that the United States would begin drawing down troops in Iraq next year. Why, five and a half years into the war, did that long-awaited announcement land with barely a thud?

Two years ago such an announcement would have been hailed with trumpets. Instead, the president’s speech at the National Defense University, a Pentagon think tank in Washington, was greeted mostly with shrugs.

The two presidential candidates, of course, reacted. It’s their job. Democrat Barack Obama told a news conference in Dayton, Ohio, that Mr. Bush’s “plan comes up short — it is not enough troops, and not enough resources, with not enough urgency.”

Republican John McCain later issued a statement reacting not so much to Mr. Bush’s announcement but to Mr. Obama’s statement, “Withdrawing U.S. troops as Iraqi forces are able to assume greater responsibility, and as our enemies in Iraq are being increasingly weakened, is the right way to bring this war to a successful conclusion.”

Maybe that’s why Mr. Bush’s announcement seemed almost irrelevant. While one Marine battalion will be withdrawn this fall and not replaced, most of the reduction won’t occur until late January, after this president has handed the problem off to his successor. And even then, there will still be 138,000 U.S. troops on the ground in Iraq, more than there were in January 2007 when Mr. Bush’s vaunted troop surge began.

The suspicion grows, too, that regardless of who wins the White House in November, much of the decision about when and how to withdraw U.S. troops will be out of his control. Mr. Obama has made much of his 16-month phased timeline for troop withdrawals. Mr. McCain, having abandoned his flippant “100-year” timeline, continues to insist on “victory.”

But in practical terms, “victory” in Iraq may look a lot like a phased 16-month withdrawal, both of them based on conditions that will be imposed in Iraq, not Washington. To the extent that the troop surge was supposed to reduce violence in Iraq, it succeeded. To the extent that it was supposed to buy time for the Iraqis to form a working, consensus government, it failed.

Iraq’s Shiite-dominated central government is feeling nationalistic, which is to say sectarian, reluctant to enroll 100,000 Sunni “Sons of Iraq” into its security forces and insisting that Iraqis, not U.S. politicians, will set the timetable for U.S. withdrawal.

Meanwhile, in northern Iraq, control of the vital oil center of Kirkuk remains an unanswered question, with Kurdish nationalists squared off against the central government.

That raises the possibility — touted over the weekend by the Democratic vice presidential nominee — that Sen. Joe Biden, D-Del., was right in May 2006 when he wrote that since Iraq eventually would devolve into three states, one Kurdish, one Shiite and one Sunni, U.S. policy should encourage the inevitable.

Clearly the United States doesn’t want 138,000 troops on the ground permanently presiding over a tripartite Iraq. As Steve Coll reported in the Sept. 8 edition of The New Yorker, some of the U.S. military’s best young thinkers now believe that “Even if Iraq holds onto its embryonic democracy, it may be settling into a state that resembles Algeria or Colombia — unstable and troubled by internal violence but secure within its borders and unthreatened by existential collapse.

“This may not be the ‘victory’ sought by Bush administration speechwriters, but for many Americans in both major political parties, after the expenditure of so much blood and treasure in a war that became a strategic cul-de-sac, it would be more than good enough.”