Republican Ruth McClung is picking up momentum, dollars and support in her unexpected surge against Congressman Raul Grijalva, but stats wiz Nate Silver remains skeptical of her chances.

Silver talks in general about the latest wave of GOP enthusiasm here. An excerpt:

Raúl M. Grijalva. Bennie Thompson. Jan Schakowsky.

Jim Oberstar? John Larson? Corrine Brown?

Peter DeFazio! John Dingell! Barney Frank!

These are some of the Democratic incumbents, most long believed to be safe by analysts. But in recent weeks, polls of their districts have suggested surprisingly competitive races.

Some of these polls show the Republican challengers leading; most show the Democrat ahead, but by a smaller margin than expected. Some of the polls are from independent researchers; most are issued by the campaigns themselves, or by other Republican-affiliated groups. Some of the companies conducting these polls have strong reputations; others have little track record.

What these polls have in common, however, is that each time one is issued, they make Republicans very excited — and Democrats very nervous. It’s time for a more sober look at them.

Sabato's Crystal Ball has moved the CD7 race from "likely Democrat" to "leans Democrat":

Raul Grijalva in AZ-7 is the trendiest dark horse GOP pick-up opportunity this week. Grijalva is a liberal Democrat, chairman of the Congressional Progressive Caucus, who represents a district that went 57% for both Obama and Kerry during their respective presidential runs. How is he endangered? One word: boycott. Following the Arizona legislature’s adoption of a controversial immigration measure in April, Grijalva signed onto the call for a national boycott of Arizona. It was a popular move among liberals, but not among Arizonans, hampered as all states have been by the tough economic times. His Republican opponent, Ruth McClung, has garnered a Sarah Palin endorsement, sure to bring national attention but also a degree of skepticism from the district’s less conservative voters. If Democrats lose here, it will be a truly needless fumble.

Read the whole thing here.