Atheists and their supporters hope for a large crowd Saturday at a daylong rally a few blocks from the White House, but it remains to be seen if the speeches and musical performances will overcome challenges to pack the pews with the faithless.

Scheduled speaker Johnny Depp, the actor caught in a messy divorce, and his wife Amber Heard, who has charged that the actor physically abused her, backed out of the event near the Lincoln Memorial late last month.

And organizers of the Reason Rally already were taking a gamble. After a similar event in 2012 attracted a crowd with a tough-on-religion approach, organizers sought to be more inclusive, and have made fewer headline-grabbing waves.

The rally is being put on by the Reason Rally Coalition, which includes four prominent organizations representing nonreligious Americans, and many more co-sponsoring groups, and has a lineup including Wu-Tang Clan members and Bill Nye, the science guy.

Lyz Liddell, executive director of the Reason Rally Coalition, a paid position she likens to a community-building pastor, says organizers were disappointed when Depp and Heard withdrew.

“We were like, ‘Wait! What?’” she says. They then learned about the abuse allegations, she says, and “we absolutely support Amber and hope they can both have success in their personal and professional lives.”

The show will go on. Added to the lineup is a second member of Congress, Rep. Bobby Scott, D-Va., who will join Rep. Tulsi Gabbard, D-Hawaii, in speaking. Their offices confirmed the lawmakers, who do not identify as atheists, will attend.

Liddell says the organizers expect 30,000 people to gather at the base of the Lincoln Memorial for the 10 a.m. to 7 p.m. event. The 2012 rally, which featured scientist Richard Dawkins, drew as many as 30,000 people, though some sources offered lower estimates.

“That [2012] event was very assertive in its pro-atheist message and not afraid to come down very hard on religion,” she says. “We did a lot of advertising and some very edgy advertising. … There were a lot of ripples preceding the event.”

A man depicts Jesus riding a dinosaur at the 2012 Reason Rally on the National Mall. BRENDAN SMIALOWSKI/AFP/GettyImages

She says organizers feel they have done a good job reaching "the angry atheist” and this year have been “declining opportunities to make a lot of waves” with the hope of drawing people who simply identify as having no religion and may be put off by controversy.

Freedom From Religion Foundation co-President Dan Barker, a pastor for 19 years before declaring himself an atheist, says “there’s a slight concern” about turnout but that he believes attendees would be motivated more by pride in atheism than seeing a celebrity.

“I went from fundamentalist to moderate to more liberal until I threw out all the bathwater and realized there was no baby,” he recalls. “It was gut-wrenching, it was like spitting on grandmother. … I had to grow up and say there’s no Santa, oops, and there’s no God, too.”

Barker is suing for the right to address the House of Representatives with a secular invocation in place of a religious prayer and on Thursday the New York Times ran a full-page ad promoting his cause.

The organizers of rallies in the nation’s capital often have overambitious expectations, but Liddell says a large base from organizations will spur turnout – along with performers including a Beatles cover band and the Gay Men’s Chorus of Washington, D.C.

But Catholic League leader Bill Donohue, well-known for aggressive push-back on criticism of the Catholic Church, says he doubts 3,000 people will show up.

“I suspect they will get far fewer people than they are projecting. … It’s a pathetic demonstration,” he says, adding: “An awful lot of onlookers are sometimes counted as participants."

Donohue says he proudly led the push for a Catholic chaplain in the House of Representatives and says members of religions foreign to the 13 Colonies should be allowed to give opening prayers. He opposes Barker’s quest to address the House but says he may be less opposed to someone he views as less combative.

“These people stand for nothing, most of them are good for nothing, they are not content to say ‘different strokes for different folks,’” he says. “Are they engaging in groupthink? I thought they were ‘freethinkers’ but I don’t know.”

Attendees listen at the 2012 Reason Rally on the National Mall. Allison Shelley/Getty Images

Donohue says he won’t encourage counterprotests, but local evangelists do often target such events. A rally originally billed as “the Million Muslim March” in 2013 drew a few Muslims and academic Cornel West, who were trailed around the National Mall by megaphone-wielding Christians who, while toting enormous crosses, ridiculed the attendees and urged conversion.

“I’m very embarrassed by those people,” says Ray Comfort, leader of the Christian outreach organization Living Waters, who organized what may amount to a large counterprotest effort this weekend. He says he signed up 1,000 Christians to engage the nonreligious and distribute $25,000 in Subway gift cards to atheists.

Comfort’s tone would surprise many. He says he has the personal cellphone numbers of some of the atheist event’s leaders and swaps friendly text messages. He recalls a fond memory of being flown out to an American Atheists conference in 2001, where he signed copies of his books, and says he enjoys engaging the nonreligious in conversation.

Comfort says he applied for a filming permit for the base of the Washington Monument for Saturday afternoon, where he hopes to interview atheists about their reasons for disbelief, but says authorities told him 1,000 attendees would cross the line into a demonstration, so he revised down the number and nixed the gift card giveaway, which he says instead will benefit the homeless in Los Angeles.

But Comfort still intends to give away 5,000 copies of his book "Fat Chance: Why Pigs Will Fly Before America Has an Atheist President" and says many of the people who signed up to help probably will still come, though he hopes they won’t heckle the atheists.

“I think the vast majority will still come,” he says. “Because we disinvited them, they will come of their own volition and no permit is necessary. We won’t be gathering as one big group, and they will be able to chat with atheists and share ideas.”

Comfort says he believes there’s scientific proof of God’s existence and that many atheists are irreligious because they weren’t shown enough love. He says “we’re nothing like the Westboro Baptist Church, I’d want to go to the other end of the Earth to get away from those people.”

Speakers at the atheist rally will address a range of issues, notably including advocacy of science-based sex education in schools and evidence-based responses to climate change, Liddell say. Recent controversy over whether transgender people can use public restrooms of their choice also will be addressed.

“Our goals are not to impose atheism on the country, our goals are to have policies that are based in reason,” she says.

Whether the steps by atheists to be more respectful of the religious, and vice versa, will be a good or bad thing for turnout remains to be seen.