Former Iowa first lady Christie Vilsack (D) will not challenge Sen. Chuck Grassley (R-Iowa) next year, the Des Moines Register is reporting.“I have decided not to run for the United States Senate in 2010,— Vilsack, a lawyer and educator, said in a statement e-mailed to the state’s largest newspaper. “I will continue my work with the Iowa Initiative to Prevent Unintended Pregnancy and will be active in our Party and across the state in issues that affect the quality of life for all Iowans.—Vilsack, who is married to current Agriculture Secretary and ex-Iowa Gov. Tom Vilsack (D), said she was “flattered and humbled by the requests from Democrats, Independents and even some Republicans to consider running.—Christie Vilsack’s announcement paves the way for lawyer Roxanne Conlin to soon join the Democratic primary and become the frontrunner in a race that already includes Tom Fiegen and Bob Krause, both former state legislators.Democrats have promised a vigorous challenge to Grassley, a veteran Iowa officeholder seeking a sixth Senate term.