Likely Republican presidential nominee Donald Trump has the support of white evangelical Christians, but it is far less than the support the group extended to previous GOP presidential candidates, a new survey showed.

The lukewarm endorsement of white evangelical Christians, a crucial bloc of Republican voters, could undermine Trump's chances of winning the White House in November, according to Religion News Service (RNS).

Less than five months before Election Day, presumptive Democratic nominee Hillary Clinton is still leading Trump by six points, 43 percent to 37 percent, basically unchanged from a month earlier, a new CBS News poll showed.

The survey, released Wednesday, also showed white evangelicals supporting Trump 62 percent to just 17 percent for Clinton.

That might look impressive at first glance but it actually pales in comparison to the support extended by white evangelical voters to previous Republican presidential candidates, RNS says.

In the previous three presidential elections, George W. Bush won 79 percent of the white evangelical vote in 2004; John McCain won 73 percent in 2008; and Mitt Romney – the first Mormon to head a major party ticket – also won 79 percent in 2012.

Trump needs a strong turnout from that faith-based group to win, given his high negative ratings and vulnerabilities as a volatile, first-time candidate, RNS says, adding that the latest poll figures are not encouraging for Trump.

Many prominent Christian conservatives have expressed their opposition to Trump's presidential bid, citing his brash manners, personal history and apparent inability to speak articulately about his faith, which have reportedly raised suspicions among evangelicals.

Last year, Trump raised eyebrows when he gave a large audience of evangelicals a sampling of his religious practices.

"When we go in church and I drink the little wine, which is about the only wine I drink, and I eat the little cracker—I guess that's a form of asking forgiveness," he said.

Trump has long been exerting efforts to win more support from conservative Christians.

On June 10, Trump spoke at the annual conference of the Faith and Freedom Coalition in Washington, D.C. where he vowed to "respect and defend Christian Americans."

On June 21, Trump is scheduled to attend a gathering in New York City of leading social conservatives from around the country.