For a president who has faced so much bad news all year, it must have been a massive relief to save a congressional seat and kill a top terrorist in a single week. And both developments show the political danger for Democrats who think they will gain ground by default.

As low as he stands in the polls, more good news from Iraq could restore George W. Bush’s momentum. The bottom dropped in the president’s approval ratings when independents and a surprisingly large number of Republicans began losing faith in his handling of the war. It is doubtful that so many conservative-leaning Americans had suddenly become pacifist hippies. Instead, Bush lost their backing because it appeared we were losing the war in Iraq — that we were merely reacting to events and not setting the agenda.

The June 7 air strike that killed Abu Musab al-Zarqawi, the al Qaeda leader in Iraq, was the sort of event that could make a difference for those Americans who have supported the war but who feel we are adrift, despite predictions that in the long run Zarqawi’s death will not significantly slow the pace of insurgent violence.

At a minimum, the demise of Zarqawi and several members of his gang gave Bush a reason to end what had almost become a deafening silence from the White House on the subject of Iraq. For weeks now he and his aides have cycled through a series of topics, from energy to immigration, in hopes of keeping the endless stream of bad news from Iraq off the front pages. Most recently, the investigation of Marines suspected of wrongfully killing civilians in Haditha threatened to overcome Bush’s desire to avoid talking too much about Iraq.

Even if killing a top terrorist ultimately changes little on the ground in Iraq, at least it gives the appearance that the U.S. military is not just sitting around waiting to get blown up. And coming at the same time as Iraq installed defense and security ministers, the successful U.S. strike could become a turning point toward a stable Iraq that runs itself.

Such a turnaround would surely be enough to push the president above the 40 percent watermark in approval ratings, a symbolic threshold for effectiveness in the White House. Even if it is just a temporary boost, it would end his losing streak of staying below the 40 percent marker for more than three months, an untenable record not seen since the days of Jimmy Carter and Richard M. Nixon.

For Republicans on Capitol Hill, saving the congressional seat in San Diego was perhaps even better news than a prize killing in Iraq. Sure, it was a conservative-leaning district, but this was the seat vacated by the imprisoned Randy “Duke” Cunningham, a GOP poster boy for what the Democrats have been calling his party’s “culture of corruption.”

Democrats must face up to the fact that if they cannot win the seat of a Republican so recently sent to jail for corrupting his office, then their hopes for riding the scandal coattails back into power could be a pipe dream.

The news was not all good for Bush in the wake of Republican Brian P. Bilbray’s narrow but clear victory in California’s 50th District. His return to Congress, where he served from 1995 through 2000, was due in no small part to his high-profile opposition to the president’s pro-guest worker stance on immigration. Bilbray’s outspoken hard line against relaxing immigration laws provoked Sen. John McCain, R-Ariz., a Bush ally on naturalizing illegal aliens, to cancel a fundraising appearance in the final days of the campaign.

Still, it was an overall plus for the president to see his party survive the special election, which could have spelled doom for the GOP in November had it gone the other way.

Democrats now must consider the possibility — no matter how remote — that the midterm election will occur in an environment where Iraq is looking up and Republican scandals are fading away. What then? Despite advice from some party consultants that the best campaign strategy would be to keep the slate clean of a specific agenda, Democrats might have to take more initiative.

It is not true that Democrats have said nothing about what they would do if the voters put them back into control of Capitol Hill, but they certainly have not marketed an agenda in the way that Republicans did in 1994 before they won power in the House and Senate. House Minority Leader Nancy Pelosi, D-Calif., did lay out some objectives last month in a memo to supporters, saying her first priorities in a Democratic-controlled 110th Congress would be raising the minimum wage, implementing all the recommendations of the Sept. 11 commission, cutting subsidies for oil companies, reducing student loan rates and making prescription drugs more affordable.

Last week’s news from San Diego and Baghdad prove that Pelosi might want to build on that memo and give Democrats a specific platform to run on.

Contributing Editor Craig Crawford is a news analyst for MSNBC, CNBC and “The Early Show” on CBS. He can be reached at ccrawford@cq.com.