Former President Bill Clinton gave a long speech in Philly Tuesday designed to introduce voters to a side of his wife the country doesn't know. 

https://youtu.be/8RchVnIn_-Y?t=1m4s

The former President has stumped for plenty of other candidates, but now he faces a new challenge: going to bat for his wife of more than 40 years.

Candidate spouses and the role they play on the campaign trail has evolved in recent decades: each must find a balance between personal and political. 

For more on how that role has changed over the years, Take Two spoke to Kate Andersen Brower, author of the book "First Women: The Grace and Power of America's Modern First Ladies." 

Press the blue play button above to hear the full interview.