He said: "Evangelicals have become people with two qualities: they are both self-professed Christians and doggedly conservative politically."
Keller wrote in the New Yorker that pollsters have re-identified the term as they've highlighted a specific voting bloc, with 80 per cent of this group voting for Trump and a similar percentage for Roy Moore last week.
He added: "When they survey people, there is no discussion of any theological beliefs, or other criteria.
"The great majority of them simply ask people, 'Would you describe yourself as a born-again or evangelical Christian?' And those who answer 'yes' are counted."
The Cambridge English Dictionary defines the word as: "Belonging to one of the Protestant Churches or Christian groups that believe the teaching of the Bible and persuading other people to join them to be extremely important".
However, Keller regrets that 'evangelical' no longer refers to theological beliefs regarding the "the necessity of conversion".
He explained that the political Evangelicals, the "big-E Evangelicals", treat evangelicalism "as the civil or folk religion accepted by default as part of one's social and political identity".
He concluded to suggest genuine evangelicals may abandon the name in the future for something else, "yet be more committed to its theology and historic impulses than ever".
