The latest Rasmussen poll testing the Senate race between incumbent Sen. Charles Grassley, R-Iowa, and attorney Roxanne Conlin, a Democrat, showed Grassley leading Conlin 55 percent to 35 percent.

This is a wide gap that should be alarming to Conlin because the window of opportunity is shrinking as November approaches.

It’s true that the campaign has not really even started. The summer is a slow period when no one is interested in getting distracted from cookouts, vacations, and looking for work.

Another factor playing in this race is the power of the current office holder. Grassley has name recognition, a big staff that can help him keep in touch with his constituents, free mailing privileges that allow him to send out newsletters, polls, and other informative material, and the visibility of being one of the senior senators in Congress.

Also, Iowa has been very unkind to women candidates, and it is only one of two states that have never elected a woman governor, senator, or member of Congress. Whether this trend will continue is anyone’s guess. But in Iowa women candidates for office definitely have an uphill battle to fight.

Finally, Iowa has two very senior senators, Tom Harkin and Grassley, who have represented the state quite effectively in Washington, D.C. Many voters will look at Grassley and weigh replacing him with a new senator who has no experience, connections, or clout. Moreover, if the Republicans regain the majority in the Senate in 2010 or two years later — which is a definite possibility — Grassley would be one of the most powerful senators.

Grassley has become somewhat controversial this year, especially because he seemed to buy into the incorrect argument that the health-care bill would include “death panels” that would decide when to pull medical support, especially for the elderly. Grassley has also been identified with the new conservative wing of the GOP — perhaps even the Tea Party movement — and some think that Iowans are not that conservative.

Therefore, Grassley’s support at 55 percent is lower than it should be for such a formidable figure.

Still, this is a year that pundits, pollsters, and analysts feel will generally favor Republicans in gubernatorial races (Iowa’s Democratic Gov. Chet Culver is behind in the polls to his GOP challenger, former Gov. Terry Branstad), and Democrats are expected to lose many seats in Congress.

I have said in several talks and columns that Conlin needs to define Grassley the way she would like voters to judge him. She cannot wait for him to define her as a rich, tax-and-spend, liberal trial lawyer.

Democrats will vote overwhelmingly for Conlin. Republicans will support Grassley. This race will be about convincing non-party (so-called independent) Iowa voters that she’s the best candidate for the Senate. Independents are the “swing” voting bloc, and in every poll I have seen, they are leaning Republican in 2010.

So Conlin needs to go and speak to these voters and persuade them that Grassley should be retired from office and should go back to his farm and plant some beans and corn. If she can’t get the independent voters to turn out for her, she’s toast.

– Steffen Schmidt is a professor of political science and public policy at Iowa State University. He writes a political blog for the Des Moines Register and does analysis in Spanish for CNN en Español. He also serves as chief political and international correspondent for insideriowa.com.