Did they turn it down because they knew it would look bad Most likely, because they'd be giving up their sure chances of election to the House for a toss-of-the-dice chance at the Senate.
Nobody in their right mind would do that. It'd have to be somebody who's not currently in office.
There's nothing to lose for the congressmen. They are on the ballot regardless. If they win the Senate race, they hold a special election-- unless the Republican wins the congressional race (unlikely) against the incumbent.