Aided by public revulsion over an Internet-age sex scandal, Democrats enter the final month of an election campaign well-positioned to challenge for control of the U.S. Congress, while Republicans increasingly express concern about holding onto power.

"We're going to need everything we have to make sure we're victorious," said Republican Rep. Tom Cole of Oklahoma, who had long experience as a party strategist before his election to Congress.

"I think we have the ability to do that but it depends on how well we perform," he added.

Yet with four weeks — and an unknown number of swings in political momentum — remaining until the Nov. 7 elections, when American voters will choose a new Congress and governors in 36 states, Democrats guarded against excessive optimism.

"It's still an uphill battle," said New York Sen. Chuck Schumer, speaking at the end of a tumultuous week in which Republicans struggled to overcome the political damage caused by former Congressman Mark Foley of Florida and his sexually explicit computer messages to teenage male pages.

Democratic candidates are in competitive races for seven Republican-held seats in the Senate and 30 or more in the House of Representatives, according to public as well as private polls. Equally significant is that barring a change, Republican opportunities for offsetting gains appear minuscule — only three or four House seats currently under Democratic control and one in the Senate.

Members of the leadership in both the House and Senate are among the Republicans in jeopardy — Sen. Rick Santorum in Pennsylvania and Rep. Deborah Pryce in Ohio — as Democrats look for major gains in the Northeast and Midwest.

Four Republican congressmen are in trouble in Pennsylvania. And strikingly, three more are struggling for survival in Republican-red Indiana — at the same time Sen. Richard Lugar is coasting to a sixth term without so much as a Democratic opponent.

Thirty-six states are electing governors this year. Republican Arnold Schwarzenegger leads in the polls for re-election in California, but Democrats are in commanding positions to succeed retiring Republicans in New York and Ohio.

The fate of hundreds of ballot initiatives also will be decided. Several states will vote on proposals to ban same-sex marriages and raise the minimum wage. Republicans hope the former will boost turnout in crucial congressional races, and Democrats have similar plans for the latter.

In the race for control of Congress, Democrats must gain 15 seats to wrest control of the 435-member House, and six to establish a majority in the 100-member Senate.

Strategists in both parties agree the fall campaign already has been marked by two distinct trends. The first, which began after Labor Day, saw gradual movement toward the Republicans as President George W. Bush campaigned vigorously on national security issues.

That momentum began to dissipate two weeks ago with the partial publication of a government intelligence report that cast doubt on his administration's claims of progress in Iraq.

Then came Foley's resignation Sept. 29 after he was confronted with sexually explicit computer messages he had sent to teenage male pages who work in the Capitol. In the following days, Speaker Dennis Hastert, an Illinois Republican, and other Republican leaders struggled to answer questions of when they learned of Foley's actions and what they had done about them.

"It has stopped any momentum that the president had in improving his standing, mostly because it knocked him off the front pages and it knocked security off the front pages," said Steve Lombardo, a Republican pollster.

Some Republicans canceled planned campaign appearances with Hastert, and Democrats challenged their Republican opponents to call for his resignation.

Republican Congressman Mike Simpson of Idaho said he was no longer confident the Republicans would retain power, a shift from a week earlier, when he said he was "fairly confident" they would. "It's a real toss-up, he said.

An Associated Press-Ipsos poll taken while the scandal was dominating the news found that about half of likely voters said the issues of corruption and congressional scandal would be important when they cast their ballots.

About two out of three of those voters said they would choose the Democratic candidate.