Republican presidential candidates have lowered the quality of political discourse and debate in the U.S., and made it "offensive," White House spokesman Josh Earnest said on Friday.

"I think many people have made the observation that political debate in this country in this cycle is markedly different than the kind of race that has been run in recent presidential cycles, and some of that is due to the rhetoric that we've seen on the Republican side of the aisle," Earnest said.

"There's just no denying that," Earnest responded when asked if the 2016 race will permanently alter the tenor of political campaigns.

"There were a variety of Republican candidates earlier in the primary process that had some quite shocking, controversial and even offensive things to say," Earnest said.

"There are certain aspects of our political discourse that have gotten too polarized in a way that ultimately is counterproductive and only feeds greater dysfunction in our political system," he continued.

He added that Democrats are not equally responsible for the rise in personal attacks and effort to exploit racial divides.

"I think that there is a risk of drawing an equivalence [in speech], even among the two presidential candidates, that I don't think would withstand any scrutiny at all by an unbiased analyst," he said.

"And I think that people will consider the rhetoric and language that is used by the presidential candidates to draw their own conclusions about that individual's fitness for office," Earnest added.