"...one of the country’s most divisive election campaigns in decades. "

Appears that way.  But appearances can be deceiving.  The election campaign is only--I mean only--a reflection of one of the country's most divisive ISSUES in decades: the number of non-assimilating immigrants within its borders.  

So, the statement is a lot like saying Brexit campaign was the most divisive..."  No.  the ISSUES that made sparked that campaign were the factors that divided the country.  

All campaigns do is reflect the issues.