OK, so now the Democrats have made their point by passing an Iraq spending bill that calls for troop withdrawals as early as July. And now the president will veto it.

After all this bipartisan posturing, can we finally have a serious debate about Iraq?

Now is the moment when Republicans and Democrats must focus like a laser on what must be done to prevent even greater Iraq disaster. There will be no time for Plan B if the current White House Plan A fails.

But Plan A — as currently directed by the White House — simply cannot work.

Many within the administration and the military grasp this, as does Secretary of Defense Robert Gates. Many Republican senators know it. But responsible Republicans have failed to press the White House for a better Iraq strategy. Many Democrats seem more eager to see Bush fail than fight for a workable plan.

Here's the awful truth. This isn't just Bush's war. Not anymore. White House mistakes on Iraq were huge (read George Tenet's memoir, "At the Center of the Storm," for more grim details), but this is now our war, too. We all will be stuck with its awful consequences — a failed Iraqi state, more Islamist terrorism and threats to Mideast oil — if it fails.

Yet Bush's Plan A — as now being conducted — can't work. Why so?

Plan A claims a surge will buy time for the Iraqi government to shape up. In other words, the surge is only a tactic. No matter the great talents of Gen. David Petraeus and the guts of American soldiers, military action alone cannot stabilize Iraq. Our withdrawal depends on whether the Iraqi government can fashion a power-sharing accord between Shiites and Sunnis, as Petraeus told Congress this week.

Both Republicans and Democrats talk about setting benchmarks for Iraqi Prime Minister Nouri al-Maliki. Democrats talk about making war funding dependant on his meeting those benchmarks.

But Maliki is too weak to meet those benchmarks. His party has far too few seats to get laws through the national assembly that are crucial for Shiite-Sunni power sharing.

And setting timelines for U.S. withdrawal makes Shiites and Sunnis even less willing to meet benchmarks. They know, once the Americans start to leave, the fight for power in Iraq will start in earnest. So they are reluctant to make concessions, as they gird for the coming battles.

Iraq's neighbors — Iran, Syria and Sunni Arab states like Saudi Arabia and the Gulf Emirates — sense this bigger war is coming, and more aid is flowing from these countries to Shiite and Sunni militias inside Iraq. Gen. Petraeus was right when he said a troop pullback this fall would lead to more sectarian killings.

So if Plan A won't work, and setting timelines won't work, what else to do?

Go for Plan A Plus.

Thoughtful Republicans and Democrats in Congress must press President Bush for a plan that puts Iraq's troubles into a wider strategic context. Right now the entire Mideast is expecting a wider Iraq war and this psychological dynamic makes the fighting inside Iraq worse.

The only way to change that dynamic is for the White House to embark on a serious diplomatic offensive in the region. That offensive would be aimed at convincing Iraq's neighbors their interests require them to help stabilize Baghdad. It would require broad and comprehensive talks between the United States and Iran — an approach still resisted by Vice President Cheney's office.

In such an offensive, Washington has strong cards to play. Shiite Iran and Sunni Arab states are worried that a U.S. withdrawal will lead to Iraq's collapse and will suck them into a deadly proxy war in that country. But U.S. diplomacy over Iraq has been insufficiently serious to produce a regional accord on stabilizing Iraq.

A round of regional talks were held in Baghdad in March, and another will be held next week in Egypt. Without greater U.S. boldness they will go nowhere.

Democrats and Republicans who put our security ahead of politics must try to get this message across to President Bush.

Some thoughtful Democrats, like Rep. Joe Sestak, D-Pa., who just returned from a trip to Baghdad with Sen. Chuck Hegel, R-Neb., believe that setting a withdrawal date could help get Iran to the table. Sestak, a retired U.S. Navy vice admiral, also argues, as do many senior officers, that a date certain is vital because our military is being ruined by the extended strains of the Iraq war.

These arguments are powerful. But I believe a timeline is a card best played as part of a regional negotiating process. To set a timeline before such talks would weaken the U.S. hand and intensify the fighting inside Iraq.

However, if Republicans don't want a timeline, responsible Republicans in Congress need to tell the President they can no longer support him on Iraq unless he embarks on a major Mideast diplomatic offensive, with the full weight of the White House behind it. No more Cheney versus the rest on Iraq policy.

Without a Plan A Plus, Congress may have no choice but to set deadlines. It's time for thoughtful Republicans to act.

Trudy Rubin is a columnist and editorial-board member for the Philadelphia Inquirer. Reach her at trubin@phillynews.com.