The Republican campaign sparked a controversy when party's presidential nominee Donald Trump and his running mate Mike Pence expressed contradicting views on America's North Atlantic Treaty Organization (NATO) allies.
In his vice-presidential acceptance speech, Pence said that Trump would rebuild the military and stand with the allies of the United States.
The rival Clinton campaign slammed Trump and Pence for their differences on this crucial issue.
"Ronald Reagan would be ashamed. Harry Truman would be ashamed. Republicans, Democrats and Independents who help build NATO into the most successful military alliance in history would all come to the same conclusion: Donald Trump is temperamentally unfit and fundamentally ill-prepared to be our Commander in Chief," he said.
"The President is supposed to be the leader of the free world. Donald Trump apparently doesn't even believe in the free world," Sullivan said alleging that over the course of this campaign, Trump has displayed a bizarre and occasionally obsequious fascination with Russia's strongman, Vladimir Putin.