Trying to Gauge the 'Obama Effect' in Senate and House Races

Senators and John McCain (far right) talk to reporters after they voted 62-36 to approve an overhaul of the nation's immigration laws.

Congressional races in other states could also feel an "Obama effect," if it materializes.

At least two GOP lawmakers are potentially vulnerable to Obama's coattails. One is Republican Robin Hayes in North Carolina, who won with 50 percent of the vote in his last race. Seeking a sixth term, Hayes is in a district whose voting-age population is one-quarter African-American.

The other is House Republican Steve Chabot in Ohio, who garnered 52 percent of the vote two years ago and now, trying for an eighth term, is also in a district that is one-quarter black.

Two Democratic House lawmakers in particular are hoping for a boost. One is Rep. John Barrow of Georgia, who got 50 percent of the vote in 2006 and is competing for a third term in a district that is 38 percent African-American. The other is a newcomer, Rep. Donald Cazayoux of Louisiana, who is in a close race for re-election after a narrow 49 percent-to-46 percent win in a special election last May. His district has a voting-age population that is 31 percent African-American.

As for McCain, there's not much chatter about prospective coattails. Jennifer Duffy, a senior editor at The Cook Political Report, says the Republican nominee is a candidate whom GOP moderates and conservatives sharing the ticket can embrace, "so the effect is he doesn't hurt them."