The number of Christian registered voters in the US has fallen sharply since 2008.
Latest figures from the Pew Research Center show a 15% drop in the last 12 years.
In 2019, nearly two thirds of registered voters (64%) identified as Christian, well below the 79% who said the same in 2008.
The biggest drop can be seen in the Democrats, with Christian voters falling dramatically from 73% in 2008 to only 52% last year.
In the same time period, the share of religiously unaffiliated voters rose sharply from 15% to 28%.
The proportion of religiously unaffiliated Republicans rose from 9% to 15% but Democrats saw an even bigger increase, with support among the 'nones' increasing from 18% to 38%.
Christian support has been important to Donald Trump over the last four years of his presidency. He wooed them in 2016 and countinued to court their favor during his time in the White House.
Exit polls for Tuesday's presidential election showed strong support for Trump among white evangelicals, with 76% giving him their vote compared to just 23% who chose Democratic rival Joe Biden.
Votes are still being counted but the evangelical support may not have been enough to secure a second term for Trump.