From Huffington Post:
“God bless America” has become the expected way for U.S. presidents to end official speeches. But that wasn’t always the case, explain David Domke and Kevin Coe, authors of the book The God Strategy: How Religion Became a Political Weapon in America.
The first president to say it was Richard Nixon, who dropped the phrase during an attempt at damage control for the burgeoning Watergate scandal on April 30, 1973.“Tonight, I ask for your prayers to help me in everything I do throughout the days of my presidency,” he said. “God bless America and God bless each and every one of you.”
The phrase didn’t catch on during the Gerald Ford and Jimmy Carter years, but Ronald Reagan’s presidency definitively ushered in the era of “God bless America.” Reagan used the line when accepting the Republican Party’s presidential nomination in 1980, and made it his standard sign-off once in the White House. Since then, it’s become a standard part of the language of the American presidency.
Domke and Coe note that out of the 229 major Presidential speeches from the inauguration of Franklin Roosevelt in 1933 to the end of Carter’s term in 1981, Nixon’s use of “God bless America” was the only the time a president used the phrase publicly. In contrast, from the inauguration of Reagan in 1981 to the Bush administration in 2008, 49 out of 129 major presidential addresses used the line.