President Barack Obama is set to deliver the annual State of the Union address tonight — and following tradition, it’s likely he’ll end the speech with three familiar words: “God bless America.”

This phrase — well known in American culture — has been present in official presidential addresses for decades.

The History Behind U.S. Presidents Using God Bless America in Official Speeches

FILE – In this Feb. 12, 2013, file photo, President Barack Obama gives his State of the Union address during a joint session of Congress on Capitol Hill in Washington. (AP Photo/Charles Dharapak, Pool)

“God bless America” and its derivatives didn’t regularly enter the presidential fray until April 30, 1973, when President Richard Nixon used it in the midst of the Watergate scandal, The Huffington Post reported.

While that was the beginning, it wasn’t until President Ronald Reagan regularly began using it that the term caught on. Ever since, it has been a standard remark made in the conclusion of many official presidential speeches.

This was the very subject of “The God Strategy,” a book written by David Domke and Kevin Coe that was published back in 2008. The text highlights how political leaders have invoked both faith and God in their speeches over the past 75 years.

In an official description of the book, the authors claim that “religious signals” have intentionally been sent by both Democrats and Republicans, particularly since Reagan’s election in 1980.

But it was Nixon’s decision to employ the word that really kicked off the use of “God bless America,” with Domke and Coe calling it unprecedented and “the first time in modern history that it had happened,” according to an article they wrote for Time back in 2008.

Speaking to the nation from the Oval Office to directly address the Watergate scandal, Nixon appealed for the nation to pray for him before uttering “God bless America.”

“I ask for your prayers to help me in everything that I do throughout the days of my presidency,” he said.

The trend continued from there.

From 1933 through 1981, of 229 major presidential addresses, Domke and Coe said that only one — Nixon’s address — included the words “God bless America.” But from Reagan’s inauguration in 1981 through President George W. Bush’s final term in office, of 129 major presidential speeches, “God bless America” was uttered 49 times.

Obama, too, has continued the tradition. Watch his 2013 State of the Union address below (see the “God bless these United States of America” reference at the 1:14:15 mark below):

It’s not as though presidents never made references to God before Nixon. Many did, but the authors argued that they hadn’t done so with as much frequency as we’ve seen over the past few decades.

“God bless America,” the authors argued, has lost its meaning over the years and has been treated by presidents as a way to “sate the appetites of those in the public and press corps who want assurance that this person is a real, God-fearing American.”

Regardless of how or why presidents of late have used the term, its history is intriguing.

(H/T: Huffington Post)