Former US president Donald Trump urged evangelical Christians Saturday to vote en masse for him in November, vowing to "aggressively" protect their religious freedom if he is elected.

The ex-leader, who rarely appears in church himself, has built a crucial base among the religious right, promising -- and delivering -- on some of their biggest priorities, including by appointing Supreme Court justices who helped overturn the federal right to abortion.

"The evangelicals and the Christians, they don't vote as much as they should," Trump told hundreds of supporters at a Washington conference put on by the Faith and Freedom Coalition, a conservative advocacy group.

"They go to church every Sunday, but they don't vote," he said, adding in a half-joke that "in four years, you don't have to vote. Okay? In four years, don't vote. I don't care."

Trump would be ineligible to run for president in 2028 because of term limits.

Evangelical voters were crucial for Trump's 2016 victory and again in his failed 2020 campaign, when 84 percent of white evangelical Protestants voted for him, according to the Pew Research Center.

Trump promised to protect their interests Saturday, as he vowed to "aggressively defend religious freedom."

"We will protect Christians in our schools, in our military, in our government, in our workplaces, in our hospitals and in our public square," he told supporters.

He additionally promised to create "a new federal task force on fighting anti-Christian bias" that would investigate supposed "illegal discrimination, harassment, persecution" of US Christians.

Almost half (49 percent) of Americans believe that religion's influence is declining in the United States and that this is a bad thing, according to a Pew Research survey published last month.

The number of Americans identifying as Christian has dropped from nearly 90 percent in the 1990s to less than two-thirds of the population in 2022, mostly due to rising numbers of people who are not religiously affiliated.

For many white evangelical Christians -- a conservative denomination that makes up about 14 percent of US voters -- it is crucial that religion stays relevant in public life.

Trump told the crowd that the political left wanted to "silence you, demoralize you, and they want to keep you out of politics."

"They don't want you to vote, that's why you have to vote," he said, adding "if you vote, no, we cannot lose."

Trump will face his Democratic rival, President Joe Biden, in the first 2024 presidential debate on Thursday.