The 2016 Presidential race may appear wide-open at the moment, but the continued trend toward extreme negative partisanship has already established the basic boundaries and expectations for this presidential election cycle, according to a new paper by Emory University political scientist Alan Abramowitz and Emory political science graduate student Stephen Webster.

"The most important influence on the 2016 presidential election as well as the House and Senate elections will be the division of the American electorate into two warring partisan camps," Abramowitz and Webster write in "The Only Thing We Have to Fear Is the Other Party," posted June 4 on the Center for Politics' Crystal Ball site.

Abramowitz and Webster found that for a growing percentage of American voters, negative feelings toward the opposing party outweigh positive feelings toward their own party.

They note that most of this change has occurred since 2000: Between 2000 and 2012 the proportion of positive partisans — voters who liked their own party more than they disliked the opposing party — fell from 61 percent to 38 percent while the proportion of negative partisans — voters who disliked the opposing party more than they liked their own party — rose from 20 percent to 42 percent. 

And it's not expected to end anytime soon, they say: "Exceptionally high levels of party loyalty and straight-ticket voting combined with increasing reluctance to openly identify oneself as a party supporter reflect a fundamental change in the way Americans relate to the Democratic and Republican parties — the rise of negative partisanship."