Washington ? One way to look at the National Intelligence Estimate on Iraq released this week is to review what it describes as the best-case scenario.

In that scenario, Iraq’s security will improve modestly over the next six to 12 months, but violence across the country will remain high. The U.S.-backed central government will grow more fragile and remain unable to govern. Shiite and Sunni Muslims will continue their bitter feuding. All sides will position themselves for an eventual American departure.

In Iraq, best-case scenarios have rarely, if ever, come to pass.

Four and a half years after President Bush ordered the invasion of Iraq, and after countless strategies, plans and revisions have failed to pacify the country, Bush next month faces what may be the final major decisions he can make about the war.

But even before top U.S. commander Gen. David Petraeus and Ambassador Ryan Crocker report to Congress, now set for Sept. 11, the president appears hemmed in by decisions he and others made months or years ago.

His generals are calling for troop cuts in Iraq because the strain has limited the Army’s ability to respond to other crises. There is widespread agreement that the additional 28,000 U.S. troops dispatched under the so-called surge will have to begin coming home in April when their 15-month tours will start to end.

Bush’s one-time hope in Baghdad, Prime Minister Nouri al-Maliki, who was installed in April 2006 after intervention by Secretary of State Condoleezza Rice, has stuck to a narrow Shiite agenda. Al-Maliki has failed to unify the government, improve basic services or pass major legislation.

There has been growing speculation – fueled in part by Bush’s own words this week – that the United States might be preparing to engineer al-Maliki’s ouster. Rumors of a coup swept Baghdad this week, and several U.S. senators have jumped on the dump-al-Maliki bandwagon.

But even if al-Maliki were replaced, it’s hardly certain that that would make much difference.

Al-Maliki has carried out the will of Iraq’s dominant but long-suffering Shiites to exert political power. Any other leader would have to do likewise.

During the Vietnam War, U.S. presidents hoped that one South Vietnamese leader after another would strengthen that country. None ever did.