Worth mentioning that Duckworth is currently pregnant, and it's believed that is what the main thing stopping her from running is.
I think she steps aside for now.
Isn't she a little bit.... old?
She is 46.
I really don't think Duckworth is a particularly strong candidate, and I really don't think Madigan even has a Senate race on her radar. The three Democrats Kirk should be worried about are Bustos, Frerichs, and Simon, and in that order.
Simon would lose, he should worry about Quigley, Frerichs, and Bustos (in that order). Any of those three would probably beat him, tough an opponent as he'll be.