Colorado:Senator who defeated replacement for resigned Colorado State Senator facing tough election challenge

In 2013, Democratic State Senator Evie Hudak resigned before facing a recall vote. Under Colorado law, that meant a Democrat could replace her. That Democrat was Rachel Zenzinger, who then lost the 2014 election to Laura Woods, one of the leaders of the recall effort.  That one race tipped the Senate from Democrat to Republican.

Now, there's a rematch and both parties are pouring in money for the fight.