-LRB- CNN -RRB- -- Democratic Sen. Barack Obama and Republican Sen. John McCain in August will be on the same stage for the first time in the 2008 presidential campaign . The Rev. Rick Warren says he makes no endorsements because he shepherds `` both sides of the flock . '' The Rev. Rick Warren has invited them to appear at a leadership and compassion forum in his Saddleback Church in Lake Forest , California , on August 16 . Warren , the author of the best-selling book `` The Purpose Driven Life '' spoke with CNN 's Wolf Blitzer by phone Tuesday from Sao Paulo , Brazil . BLITZER : Pastor Warren , how did you do it ? How did you convince both of them to show up ? PASTOR RICK WARREN , SADDLEBACK CHURCH : Well , Wolf , they 've both been friends for a long time . I knew both John and Barack before either of them decided to run for office , had talked with them . Both of them have helped me in the past with our peace plan and with -- they 've sent messages to Saddleback at some of our conferences . And so I just thought let 's -- you know , I might be the guy to get them together . So , I called them up and said , let 's do it . And they said , well , we 'll do it if you be the only questioner , if you do n't have a forum , do n't have a panel . And if you 'll ask all the questions , then we 'll do it . BLITZER : But they 're not going to be together . They 're going to be separate . These are going to be Pastor Warren and Barack Obama , followed by Pastor Warren and John McCain . But there 's not going to be any interchange between the two of them , is that right ? WARREN : Yes . I 'm going to -- my plan is to bring them out on stage together at the beginning or at the end . But what I want to do is I want to let each of them talk without interrupting each other . And it 's not a debate format . There will be plenty of time for debates . What I want to do is get people to know the real person like I know them without a time barrier and a buzzer and a time for rebuttal . Let them just speak what they need to say . BLITZER : The last time we spoke was right after you invited Barack Obama when he was still running for the Democratic presidential nomination . You got some criticism from a few fellow evangelicals out there . You called him in the interview with me an amazing , an amazing man , Barack Obama . Could you see yourself supporting him for president ? WARREN : Well , I do n't support anybody for president publicly . I never endorse . I never campaign . You know , as a pastor , I do n't really think that 's my role . I have to shepherd both sides of the flock . And I have a church full of Democrats and a church full of Republicans and a church full of independents . So , I think they 're both amazing men . I 've known them for a long time . They 're both very , very different . They have both different theories of government , different theories of leadership , different approaches to life . And I -- what I do is I think , because I know them , I think I can set up an environment that people can actually say , oh , so that 's what that guy 's really like . And I think I can do that for both John and for Barack .