Rev. Franklin Graham has joined other Americans in congratulating Donald Trump for his success after he swept the Indiana primary and became the Republican Party's presumptive presidential nominee on Tuesday, prompting Texas Sen. Ted Cruz to bow out of the presidential race.

Graham says he is praying that the next leader of America would be one who has great moral fortitude. "We need to continue to pray for major change in Washington and in our country through whoever is elected. Let's pray for God's will to be done and that He will give this nation leaders at every level who will look to Him for wisdom and direction," he writes on his Facebook page.

Should Trump eventually win the White House this November, the evangelist is reminding the real estate magnate that he is nothing without God. "Regardless of who your candidate of choice is—or was—remember, they are only human. Without God in the equation, they will ultimately fail. Our hope can't rest in any candidate or political party—the only hope for America is in God and His Son, Jesus Christ," he says.

Graham started his Decision America Tour earlier this year in hopes of getting more Christians involved in politics and in the elections. He writes on his Decision Magazine that there is a "sharp rift in the moral and spiritual fabric" of America because Christians are not just tolerated, but they are under constant assault for their beliefs and practices.

"In this secular age, the influence of Biblical principles and values has diminishing impact upon education, government and politics," he says. "More young people than ever before claim no religious affiliation at all."

Graham says that unless something is done about America's morality, its people are in imminent danger. "We mock God, ridicule His Word and His ways, and flaunt gross immorality. Only Almighty God can deliver us, and it is our fervent prayer as we go across America in the months to come, that He will hear our prayers and heal our land. He is our only hope," he says.