Blunt, R-Mo., wrote at least three letters helpful to Abramoff clients while collecting money from them. He swapped donations between his and DeLay's political groups, ultimately enriching the Missouri political campaign of his son Matt.
And Blunt's wife and another son, Andrew, lobby for many of the same companies that donate to the lawmaker's political efforts.
With House Republicans worried about a budding corruption scandal tied to Abramoff's favors to lawmakers, DeLay, R-Texas, announced Saturday he would not try to regain his majority leader's post in upcoming party elections.
DeLay was forced to step down last year under party rules, after he was charged with Texas felonies in a state money laundering investigation. Blunt has temporarily filled the position and now is competing to be DeLay's permanent replacement.
Blunt's own connections to Abramoff or his clients could complicate GOP plans to distance its leadership from the corruption investigation before the fall elections for control of Congress.
Abramoff pleaded guilty last week to felony charges and is cooperating with investigators whose bribery probe is now focusing on several members of Congress and their aides. As the Abramoff investigation has developed, many lawmakers have said they will donate to charity campaign contributions related to the disgraced lobbyist.
The board of Blunt's Rely On Your Beliefs Fund has voted to contribute to charity an amount equivalent to Abramoff's personal contributions, $8,500, according to Blunt spokeswoman Burson Taylor.
Blunt and DeLay and their aides frequently met with Abramoff's lobbying team and even jointly signed a letter supportive of an Indian tribe client at the heart of the Abramoff criminal investigation, according to records published by The Associated Press over the past year.
Blunt's office says all of his dealings were proper.
"Mr. Blunt has never been accused of engaging in any legislative activities on Jack Abramoff's behalf," Taylor said.
Blunt's main competitor for the House majority leader's post is Rep. John Boehner, R-Ohio, chairman of the House committee that oversees education and labor.
Boehner in 1996 admitted he distributed a tobacco political action committee's campaign checks on the House floor, but said at the time he would never do it again. He served in the House leadership in the 1990s, but lost his post after the party suffered losses in the 1998 elections.
Thomas Mann, who studies congressional issues for the Brookings Institution think tank, said Republican leaders' hardball tactics in getting legislation passed and their alliances with special interests during a decade of congressional rule are now being scrutinized by voters.
"It's been smash-mouth politics," Mann said in an interview. "They've been tough and effective in enacting their polices and they're paying a price right now for it."
Larry Sabato, a University of Virginia political scientist and author, said Blunt's name doesn't have the same nationwide recognition as other GOP leaders, and one way he could shed any ethical questions would be to support lobbying reforms.
Blunt, in a written statement, pledged to do just that.
He said that if elected leader, he would "move swiftly to enact new lobbying reforms and enhanced penalties for those who break the public trust."
Texas prosecutors recently subpoenaed records of a series of financial transactions in 2000 between DeLay and Blunt that were highlighted in a recent AP story.
DeLay raised more money than he needed to throw parties at the 2000 Republican National Convention and sent some of the excess to Blunt through a series of donations that benefited the causes of both men.
After transfers between political organizations, some of the money went to the campaign of Blunt's son, Matt, in his successful 2000 campaign for secretary of state. Now the Republican governor of Missouri, Matt Blunt eventually received more than $160,000 in 2000.
Taylor, the Blunt spokeswoman, denied that DeLay raised excess money for the purpose of transferring it to Blunt. Rather, she said, the convention fundraising was a joint effort between DeLay and Blunt all along.
She said Blunt's Rely On Your Beliefs Fund contributes annually to the Missouri Republican Party, but doesn't specify how the money should be spent.
"It stands to reason that the party committee would contribute to a Republican candidate for statewide office, in this case, Matt Blunt," Taylor said.
Both DeLay and Blunt forged strong connections with corporate lobbyists, raising questions of whether the lobbyists influenced legislation in return for their contributions. DeLay was admonished in 2004 by the House ethics committee for creating the appearance of connecting energy industry donations with legislation.
Blunt's wife, Abigail Perlman, is a lobbyist for Kraft Foods, part of Altria, the company that also includes Philip Morris. The parent firm and its companies have contributed nearly $224,000 to Blunt's political organizations since 2001, according to figures compiled by a campaign finance tracking firm, Political MoneyLine.
Blunt's supporters also included companies that have been clients of another of Blunt's sons, Andrew. He lobbies the Missouri legislature.
"He and Mr. Blunt have no contact on legislative issues," Taylor said of the father-son relationship.
She added, "Mrs. Blunt does not lobby the House of Representatives, and Mr. Blunt would recuse himself from voting or working on any issue that would impact Altria specifically."
Shortly after Blunt became the party whip in 2002, he tried to quietly insert a provision benefiting Philip Morris USA into the bill creating the Homeland Security Department.
Taylor said the provision would have cracked down on the illegal sale of contraband cigarettes, a documented source of funding for terrorist organizations. Bipartisan legislation to achieve the same result has passed as part of the USA Patriot Act, she said.
In his ties to Abramoff, Blunt was among nearly three dozen members of Congress, including leaders from both parties, who pressed the government to block a Louisiana Indian tribe from opening a casino. The lawmakers received donations from rival tribes and their lobbyist, Abramoff, around the same time.
Blunt received a $1,000 donation from Abramoff and $2,000 from his lobbying firm around the time of a May 2003 letter he wrote to Interior Secretary Gale Norton on the casino matter. A month later he signed another letter on the issue along with DeLay and House Speaker Dennis Hastert, R-Ill.
Taylor responded that Blunt "has a long history of opposition to Indian gaming. His district, which includes Branson, Missouri, is fundamentally opposed to the expansion of gaming, and he reflects that broad opinion."
She said Blunt signed the letters to Norton at the request of Rep. Jim McCrery, R-La., not Abramoff.
"It is also very important to note that Mr. Blunt does not accept campaign contributions from Indian gaming interests, so any 'quid pro quo' argument is baseless here," Taylor added.
In spring 2000, an Abramoff client accused of running a sweatshop garment factory in the Northern Mariana Islands donated $3,000 to Blunt's political organization. The company, Concorde Garment Manufacturing, paid a $9 million penalty to the U.S. government in the 1990s for failing to pay workers overtime. The company was visited by DeLay.