why did Harkin traditionally get Grade A opponents while Grassley was always given a free pass?

[RobertPlant]

It just doesn't seem fair. In the past four reelection bids Grassley has never gotten below 66%. While he is popular it was ridiculous he was getting that much votes. Why couldn't the democrats have ran someone like Berkley Bedell or Neal Smith? Harkin on the other hand always had more difficult races and usually won between 51-54% in his first three reelection bids. He always got legitimate opponents like Tom Tauke, Jim Lightfoot (who got very close) and Greg Ganske. Harkin's reelection in 2008 was the first real landslide he won and even then thats 4 points below Grassley's smallest reelection victory (66% in 1986). Grassley is used to 99 county wins (yes even Johnson County) and even in 2008 when Harkin got 62%, he still lost five counties to that Reed guy.