The leader in the Illinois Republican Senate primary fended off fresh questions Sunday about his divorce files as the Democratic front-runner got an emotional endorsement from civil rights leader Jesse Jackson and visited black churches.

Primary voters on Tuesday will choose Republican and Democratic candidates to succeed retiring U.S. Sen. Peter Fitzgerald (search), a Republican.

In Springfield, Republican leader Jack Ryan (search) again refused to make public the contents of sealed child-custody papers stemming from his divorce from actress Jeri Ryan (search).

He told reporters the papers are sealed to protect his 9-year-old son and said he didn't believe they contained damaging information.

"I don't think anything to do with my son or my family should be part of this campaign," Ryan said. "They are not running for office. It's just me."

Meanwhile, standing in front of a Chicago church choir, Jackson endorsed Barack Obama (search) and recalled how Congress passed the landmark Voting Rights Act 39 years ago after civil rights marchers outside Selma, Ala., were met with dogs and police clubs.

"We must never forget the blood of the cross or the blood on the bridge at Selma, Ala.," Jackson said. He urged his audience to "vote to have a black man of substance in the U.S. Senate."

Obama, leading in all recent polls, sought to fire up supporters to produce a big turnout Tuesday, saying, "I need you to carry me across the finish line." Obama, the son of a Kenyan father, dismissed any notion that his unusual-sounding name would be a handicap.

"If we can elect a governor named Rod Blagojevich (search) we can elect a senator named Barack Obama," the Harvard-trained former civil rights lawyer said.

The pressure on Ryan to unseal the documents intensified as another Republican candidate, Jim Oberweis, called on Ryan to "clear the air."

Oberweis suggested Sunday that former Gov. Jim Edgar (search), state GOP Chairwoman Judy Baar Topinka or Cardinal Francis George of Chicago could view the records and assure voters there was nothing of concern. At a Republican dinner in Peoria, Oberweis met briefly with Ryan to discuss the proposal, but Ryan turned it down.

Republican officials have said they fear Ryan will win the primary only to have the papers become public anyway and that they could wreck his candidacy if the content is embarrassing.

"If he's the nomination of our party, there's no doubt that it's going to be disclosed. That's just the way things happen in politics," said U.S. Rep. Ray LaHood of Peoria, who backs Andy McKenna in the Senate race.

In an editorial Saturday, the Chicago Tribune said Ryan should release the documents.

A Copley News Service poll released Sunday showed Obama with 37 percent, Dan Hynes with 18 percent, trader Blair Hull with 16 percent, and other Democrats in single digits.

Among Republicans, it showed Ryan with 45 percent, McKenna with 12 percent, Oberweis with 11 percent and all others in the single digits.

The telephone survey of 400 probable voters had a margin of error of 5 percentage points. It was conducted Monday through Wednesday, before the controversy over Ryan's records heated up.