For a while in 2001 it looked like the tragedy of the 9/11 terrorist attacks might bring the country together and end the political partisanship and bickering that has dominated this country for too long. It didn’t.

Write David Broder and Dan Balz in The Washington Post:

It was the moment that was supposed to change everything. But almost five years after the terrorist attacks of Sept. 11, 2001, American politics has reverted to many of its old habits and patterns.

The bipartisanship that appeared spontaneously in the aftermath of the attacks was quickly swallowed up by a resurgence of partisan differences among voters and politicians. National security emerged not as a source of unity, but as a new fault line between the two parties, creating a set of issues that have led to bitter disagreement.

The events of Sept. 11, 2001, and their aftermath played out in two national elections, in 2002 and 2004, as President Bush and his team skillfully used the issue of terrorism to expand Republican congressional margins and to retain the White House. And with midterm elections looming in November, Sept. 11 still resonates politically, with fears of terrorism and memories of a nation bound together in shock and sadness capable of affecting the attitudes of some voters.

But in the intervening period, the war in Iraq has assumed a far more prominent role in the political debates and in shaping what have become the negative views of Bush’s presidency that have defined much of his second term.

Whether the return to national rancor and partisan conflict was avoidable or inevitable remains a topic of debate, although the evidence tilts in the direction of inevitability. The deep divisions that produced the disputed election of 2000 never disappeared and quickly reasserted themselves shortly after Sept. 11. In a 50-50 America, the lust for political advantage overwhelmed calls for consensus and cooperation.

More fundamentally, the reemergence of security issues highlighted long-standing and heartfelt differences between Republican and Democratic voters over the use of military force and American power to deal with threats old and new. Once Bush fixed his eye on taking out Iraqi President Saddam Hussein, there may have been no way to avoid the political clashes and subsequent divisions that followed.

Today, the war in Iraq and the economy’s mixed signals rank higher than terrorism as voting issues. Public attitudes on Iraq are by now well fixed, to the detriment of the president. Those on the economy are subject to change, depending on whether the dominant news of the summer and fall is good or bad.

While terrorism remains a constant threat, it has subsided in the minds of many voters as the principal issue that will determine their vote in November.