After six months on the job as the head of the White House Office of Faith-Based and Community Initiatives, the 43-year-old was worn down from a feverish pace of persuading Congress to pass the president's plan giving religious groups greater access to federal money to help the poor.
He was tired of the unrelenting attacks from the left, right and center. He was tired of being away from his wife and three children.
A few days later, DiIulio confided to a top aide, David Kuo, that he was worried about his health.
Even before the president personally asked him to launch his signature initiative in January, DiIulio's doctors had advised him not to teach that spring at the University of Pennsylvania. He should take time off to lose 60 to 100 pounds, they said, and reduce stress.
But DiIulio, described by one friend as ''Newman (of television's 'Seinfeld') with a 250 IQ, a longshoreman's personality and the heart of Mother Teresa,'' could not refuse the president.
After talking with Kuo about his health, the aide called John Bridgeland, director of the White House Domestic Policy Council, and told him to come over to DiIulio's office in the Old Executive Office Building right away. The three men barricaded themselves in DiIulio's living-room-sized office. No phone calls. No beepers. No interruptions.
For the next two hours they discussed DiIulio's dilemma: Should he go home or should he serve the president and risk his life?
Even though DiIulio is a lifelong Democrat, he and the president share a common belief that the most effective defense against poverty is instilling faith in people that they can change their lives.
To DiIulio, whose father never went past eighth grade and whose mother sold dinettes at a department store, working closely with the president was a measure of how far a kid from South Philly could go in the United States.
''It was an out-of-body experience,'' he said. ''I don't know why I have been so blessed.''
The three men had tears in their eyes as they talked about the options, what his departure would mean to the faith-based initiative and how to create a smooth transition.
''I told him that his health and his family have to be his priorities,'' Bridgeland said. ''But for his health, I would be doing everything that is humanly possible to get him to stay because he embodies everything that the issue is about --- compassion.''
The difficult part was that DiIulio felt that by running the faith-based office he was following the mission that God wanted him to follow.
In the late 1980s and early 1990s, DiIulio said he lost his sense of ''mission.'' He was writing hawkish articles on crime that suggested that there was a new class of violent youths, ''superpredators'' as he called them, who didn't care about killing.
''I realized that I was wrong and I felt in my heart there had to be something bigger to do,'' DiIulio said.
That something was finding a way to reach children before they got into trouble, before they got into the hands of hardened criminals who would use them to sell drugs or do their killing for them.
As he thinks back over his time at the White House, DiIulio said he has known since early July that it was time to leave. He just didn't want to go before accomplishing what he had set out to do: pass legislation in the House, finish internal audits of five federal agencies identifying funding barriers faced by religious groups and build a strong relationship with the Corporation for National Service.
''It was tough,'' DiIulio said. ''I was trying to defy what I knew were the right things that I had to do. I was putting it off, putting it off. I knew I had to stop running myself physically into the ground and stop denying the fact that I desperately wanted to be back with my family.''
DiIulio said he had to put aside the hubris he finds so common in Washington to realize that he is not so central to the program that it could not go on without him. ''You can fall into that trap in this city,'' he said.
In addition to his health and missing his family, DiIulio was frustrated by the maelstrom over giving religious groups federal money.
To him, it seemed like a no-brainer. Churches, synagogues and mosques were already feeding, sheltering, counseling and taking care of the poor. Why shouldn't they receive the same chance to compete for federal funds as community groups?
DiIulio was disappointed when the House passed a scaled-down version of legislation embracing the president's initiative July 19. The president's plan called for giving nonitemizers the right to claim a tax deduction for donations to charities that help the poor.
The House gutted the provision by placing a cap on the deduction that was so low that critics said it would render the deduction meaningless.
''The most robust version of that would have been the best version,'' DiIulio said. ''To have that reduced down was a real body blow.''
DiIulio said he was also frustrated with the way Democrats rejected expanding ''charitable choice,'' the heart of the president's initiative. First passed by Congress as part of the 1996 Welfare Reform Act, the provision allows religious groups to receive federal money for social services without requiring them to hide their religious character.
Congress had approved the provision in three other pieces of legislation, yet Democrats were suddenly balking at supporting it. DiIulio believed it was because the initiative came from a Republican president.
''I was just flabbergasted,'' DiIulio said. The final language was almost identical to the 1996 charitable choice language signed by President Bill Clinton and supported by many Democrats, he said.
DiIulio said he kept thinking, ''Hey, for goodness sake, maybe we don't agree on the specifics, but, gosh, don't give up the core of the idea.''
''For the Democrats to be so rancorous and sound so hostile to godly people in the public square just didn't make sense,'' DiIulio said. ''It will come back to haunt them unless they succumb to the good leadership of Sen. Joe Lieberman and others on this issue.''