"They understand who Hillary [Clinton] is and they understand that Donald Trump is a threat to everything they care about," the Virginia senator said in an exclusive interview with ABC News' Robin Roberts on "Good Morning America" today.
"We got to pull it together to win," he added.
Kaine, who officially accepted the nomination as Clinton's running mate Wednesday night, acknowledged that the Democratic National Convention began in "turmoil" with Sanders' delegates protesting a Clinton presidency. In a bid to show a unified front, Sanders moved that Clinton be selected as the party's nominee for president on Tuesday night. The motion, followed by some big names in politics throwing their full support behind Clinton, has since helped lift the tone of the convention.
Kaine said he's confident that his party would ultimately unite come election day and elect Clinton over Trump, the Republican presidential nominee.
"I was a big Obama guy back in '08 and was part of the team trying to bring everybody together," Kaine said, referring to when President Obama won the party's nomination over Clinton. "I actually think where we are now, we're farther ahead than we were eight years ago."
Kaine, 58, was born in St. Paul, Minnesota, and grew up near Kansas City, Missouri, where his father was employed as an ironworker. He graduated from Harvard Law School and began working as a civil rights lawyer in Richmond, Virginia. During his primetime speech at the convention Wednesday night, Kaine admitted he "never expected to be here."
"My mom and dad are here and they're still stunned that they got somebody in politics in the family," Kaine laughed. "My parents' strong faith background made me a real believer in helping others."
When he ran for governor of Virginia 11 years ago, Kaine made clear to voters that he personally opposed abortion but would uphold the state's law. He also initially disagreed with same sex marriage but has since changed his stance and now strongly supports marriage equality.
Kaine now calls himself "a progressive," though admittedly less so than Sanders.
"I'm a progressive in the South and that may be different than being a progressive in Vermont," he said.