Democrats, liberal historians and even a majority of U.S. voters already consider George W. Bush a “failed” or “poor” president — in fact, perhaps, “the worst president in American history.” [IMGCAP(1)]

Only a thin line of loyal Republicans, led by Bush’s departing top political aide, Karl Rove, thinks Bush will be vindicated in the end, both historically and politically.

Which is it? I think the jury is still out — and ought to be — because Bush’s place in history will depend on the outcome of the Iraq War, Bush’s signature undertaking.

If the war proves to be a catastrophe, Bush will have to be considered a failure even if it’s Democrats in Congress who deny him the victory that his backers now believe is possible.

My Fox News commentary partner, Fred Barnes of the Weekly Standard, claims that Bush should be likened to the much-reviled Abraham Lincoln of 1863, before the Union began winning victories in the Civil War.

In this vision, the U.S. commander in Iraq, Gen. David Petraeus, is a figure parallel to Gen. Ulysses S. Grant, who developed the strategy that defeated the Confederacy.

It’s conceivable, but only barely, that Petraeus’ counterinsurgency strategy could undermine the Sunni insurgency in Iraq and pave the way for a political reconciliation that produces a stable, American-allied semi-democracy in Iraq.

If this great turnaround occurs — and if the consequence is a restoration of America’s standing in the world — then Bush could yet go down in history as a near-great president on the order of Harry S. Truman, who was as disrespected in his time as Bush is now.

After the U.S. won World War II on his watch, Truman’s Gallup Poll approval rating soared to 87 percent, not far below Bush’s historic 92 percent in October 2001.

With the U.S. mired in the Korean War, however, Truman’s disapproval rating was 65 percent in 1952, just about where Bush’s is today. The highest-ever negative rating was Richard Nixon’s 66 percent just before his resignation in 1974.

Many historians now place Truman among the near-greats — along with Thomas Jefferson, Andrew Jackson and James K. Polk, who stole the Southwest from Mexico — because he launched the Marshall Plan after World War II and developed the containment strategy that ultimately won the Cold War.

Rove, in his interview with The Wall Street Journal this week, predicted that Bush’s strategies for the global war on Islamic terrorism will be similarly vindicated, as will his decision to go to war in Iraq.

Unfortunately for Bush, another scenario is more likely — a Vietnam-like scenario in which, despite late victories on the battlefield, the U.S. suffers defeat because its public and politicians lack the will to sustain the effort.

As Rove pointed out, even though Democrats forced the U.S. out of Vietnam, they suffered long-term political defeat, branded as a party that could not be trusted to mount a strong foreign policy.

Whether that occurs following a U.S. defeat in Iraq, however, will depend upon whether a Democrat elected in 2008 repeats the example of foreign policy weakness pursued by Jimmy Carter.

Bush will deserve “failed” status even if Congress precipitates failure because it’s a president’s responsibility, if he launches an enterprise as consequential as war, to execute his policy well enough to maintain public backing.

On other fronts, Bush has few accomplishments that would offset disaster in Iraq and give him a place in history above “failed.” His only lasting legacy, it appears, will be a Supreme Court dominated by conservatives.

Rove, a genuine genius as a political strategist and tactician, nearly produced another legacy — lasting domination of U.S. politics by the Republican party. GOP Congressional victories in 2002 and 2004 were historic.

But it all fell apart in 2006 and Democrats are again ascendant, though not yet dominant. The causes were two portfolios that Rove had little to do with — Iraq and White House communications.

Bush and Rove had some grand domestic policy visions — topped by an “ownership society” and education and immigration reform — that failed or may fail because the White House could not convince the public and Congress of their virtues.

Rove still thinks Bush will be vindicated on Social Security reform and health savings accounts — plans whereby individuals own their benefit plans and carry them as they change jobs.

But Bush failed to sell them as “compassionate conservative” ideas. Instead, Democrats succeeded with their caricature of Bush as the president of rich America determined to make it richer by divesting ordinary workers of guaranteed social benefits.

Bush’s tax cuts, favoring the rich, were designed to increase the nation’s overall wealth. Economic growth has been decent, but it hasn’t been widely shared. And Bush has done nothing to get control of the impending fiscal crisis brought on by the retirement of baby boomers.

And even though he helped keep Republicans in power, Bush could not convince them to side with him on immigration reform, which could have won the loyalty of Latinos, the fastest-growing population group.

Congress may even fail to renew Bush’s No Child Left Behind education program, a truly compassionate initiative designed to rescue poor children from failing schools, which has lost both Democratic and GOP support.

Many of Bush’s problems stem from the same source — his failure to be a “uniter, not a divider,” as he promised in 2000. As I’ve written before, instead he should go down in history as “the great polarizer.”

So Bush is on the cusp of failure, but he is not there yet. Even Democrats who hate Bush should hope he avoids that status by pulling out a victory in Iraq — simply because all of us will suffer the consequences of defeat.

As to being “the worst president in history” — as charged by many Democrats — Bush does not match James Buchanan, who encouraged Southern secession, or corruption-stained presidents such as Nixon and Warren Harding. It would take a true catastrophe in the Middle East or another terrorist attack on American soil to put him in that category. Pray that it doesn’t happen.