Former U.S. House Speaker Newt Gingrich is back in the limelight and has thrown his support to Republican presidential candidate Donald Trump.

In 2009, he released the book "Rediscovering God in America" and a film was made based on it.

In an interview with the Full Measure website, Gingrich said one cannot understand America unless he understand the importance of God to America's past leaders.

The book takes readers to monuments and memorials in Washington, D.C. where American leaders wrote about the importance of God.

"When you take 'Rediscovering God in America' and you walk around all the monuments and you start with Washington, who talks about the importance of providence, in that without providence's intervention we wouldn't have won, you go to Jefferson, who says, 'I have sworn upon the altar of God eternal hostility against all forms of tyranny over the minds of man,' and there are four quotes in the Jefferson Memorial about God," Gingrich said.

He said U.S. leaders emphasised that God is an important part of America.

Gingrich said Lincoln's "second inaugural was virtually a sermon—and which you can read standing there, it's very short—references God again and again and again, you begin to realise—despite every effort of the modern, secular left—you cannot understand America unless you understand how deeply our key leaders had felt that God was integral to the American spirit."

In the documentary "The First American," which centred on Washington, Gingrich tried to portray him differently.

"This is the guy on whom the whole country stands. This is the father of our country. This is a man who, when he died, they said was first in war, first in peace, and first in the hearts of his countrymen," he said. "So, when we decided we would do 'The First American,' we were very, very fortunate. Robert Lyons is an actor who looks like a younger Washington. Because we wanted to break away from the old man sitting there as president at the end of his career, because young people can't possibly, you know, this is like great-grandfather or grandfather --"

To many, Washington is an image in the U.S. currency and through the documentary, Gingrich said "we wanted to take him off the currency and give you the younger, aggressive—the best horseman in the colonies, a man of enormous physical strength who could break a walnut between his thumb and first finger, a great wilderness character who was literally in his early 20s starting a world war in the West, who has four bullet holes in his coat and two horses shot from under him at the Battle of Monongahela Hill."

He said Washington is "an action hero."

"And, 'The First American' is really our effort to recentre Washington at the centre of the American experience," he said.

Through his Gingrich Foundation, he said he hopes the documentary can be made available to every high school in the U.S.

The documentary can be purchased through the Gingrich Productions and he said "we're currently shopping it to several networks."

"But, I think we'll probably try to bring it up every single birthday for the next 20 years to have people see this is what America was built on: this kind of courage, this kind of work ethic, and this kind of patriotism," he added.