South Carolina Republican Trey Gowdy says that politics is "inherently divisive" and cited it as one of the main reasons he's retiring from Congress in 2018. He spoke with "CBS This Morning" about his new book, co-written with fellow South Carolina Republican Sen. Tim Scott, on how their friendship bridges divides amid political and racial tumult.

"Politics has been divisive the whole time I've been in D.C., I think its probably getting worse," said Gowdy. "But the divisiveness didn't start with Donald Trump, it started from the first day."

He added, "Politics is all about wining and I don't think there's any other relationship we have in life where our sole goal is to win by whatever means necessary."

Scott agreed with his co-author and friend, adding that while the polarization of America is real, "the hope is eternal."

Sen. Tim Scott (R-S.C.), left, and Rep. Trey Gowdy (R-S.C.) CBS News

"Hope is necessary in a toxic world. The polarization in this county must be bridged so that we are one nation, one American family focused on the ways to get back to a position of truth, honesty and believing that American exceptionalism is alive and well," said Scott.

In "Unified: How Our Unlikely Friendship Gives Us Hope for a Divided Country" the two Republicans chart their friendship, which they say was born from a particularly tragic event, the 2015 mass shooting that killed nine black churchgoers in Charleston.

Scott said he confided in Gowdy during that dark time. "He was there, he walked that road Wednesday evening with me, he attended the funeral and some of the wakes, he was a powerful force anchoring me during a time where I just thought the tragedies are back again," Scott said.

The two also explore core themes of friendship in their new book, which they say trumps everything, including politics.

"We get to pick our friends, other than family the greatest subunit our culture has is relationships and friendships," said Gowdy, adding that friendships "transcend politics."

Speaking of his own friendship with Scott, Gowdy said, "There's no rivalry. The only argument we had was my insistence was his name go first [on the book cover] because he's a United States Senator."