By CHARLES BABINGTON

Associated Press

CHICAGO -- Perhaps no one took greater comfort in the Republican Party's third straight loss of a long-held House seat this week than Barack Obama, who says the results point to clear limits in the effectiveness of attack ads he expects this fall.

The Democratic presidential candidate played a prominent role in all three special elections to fill vacant GOP seats, and he landed on the winning side each time.

In recent contests in Louisiana and Mississippi, Republicans or their allies ran TV ads linking the Democratic House nominees to Obama, warning that a vote for them was a tacit endorsement of Obama's agenda, which the ads described as very liberal. In Mississippi, ads against Democrat Travis Childers also tied him to Obama's former pastor, the Rev. Jeremiah Wright, and to House Speaker Nancy Pelosi, D-Calif.

The efforts failed, putting Democrats in House seats the GOP had considered safe, and sending waves of panic through Republican circles nationwide.

In the third race, in Obama's home state of Illinois, Democrat Bill Foster ran ads showing the senator endorsing him, and he claimed the seat long held by former House Speaker J. Dennis Hastert, a Republican.

Obama said the outcomes bode well for his expected race against Republican John McCain this fall, although he acknowledged the power of rumors that are spread mainly through the Internet about his faith and patriotism. He told reporters this week he can overcome the falsehoods if he has enough time to campaign in battleground states and let voters get to know him better.

Meanwhile, Obama practically dared Republican congressional candidates to keep linking their Democratic opponents to him.

"The same kinds of tactics that the Republican Party has been employing over the last several election cycles just aren't going to work this time," he told reporters on his charter plane after receiving former rival John Edwards' endorsement Wednesday. "I mean, they did everything they could, right? They ran Wright. They ran Obama. In Louisiana, they ran Pelosi. The same way that in previous election cycles they had run Hillary or other folks they thought would scare off voters. It didn't work."

Obama said Americans want "change in this election," and they especially care about health care, jobs, gasoline prices, college affordability and the Iraq war.

"The Republican Party better be prepared to debate issues," he said, "because that's what people are focused on right now."

Still, Obama faces several challenges, including the need to attract working-class voters who sided heavily with Hillary Rodham Clinton in many states. She beat him by 41 percentage points in West Virginia's primary this week, a shellacking Obama tried to explain to reporters.

"Part of the issue with West Virginia was, we just didn't have a lot of time to get there" to campaign, he said. "I'm not well-known there. You know, some of these e-mails and rumors that we talked about have penetrated in West Virginia more deeply than they have in some other states. Debunking that stuff is relatively simple if you are on the ground talking to people. If you're not, then it's tough."

Obama said his primary losses to Clinton in Ohio, Pennsylvania and other places do not mean he cannot carry such states in November against McCain.

"I would just take a look at where the national polls are right now," he said. "We're beating McCain handily, we're doing really well among independents. There may be concerns among some voters because they don't know me that well. And I think that the longer we campaign, and the better they get to know me and my agenda, the better we'll do."