By Adam Klasfeld, Courthouse News Service

MANHATTAN (CN) — With President Barack Obama flying to Saudi Arabia on Tuesday, relatives of those killed in Sept. 11 attacks have redoubled efforts to hold the kingdom liable for the largest terrorist attacks in U.S. history.

Their effort has also built pressure to declassify the 28 pages of the 9/11 Commission Report about alleged Saudi ties to the attacks.

In the public version, the congressional commission noted that Saudi Arabia produced 15 out of the 19 hijackers in the 9/11 attacks, and that the kingdom generally is a "problematic ally in combating Islamic extremism."

Though the commission uncovered "no evidence that the Saudi government as an institution or senior Saudi officials individually funded the organization," dozens of redacted pages detail alleged ties that have been censored for more than a decade.

Families and legislators have tried since the attacks to learn more, only to be rebuffed by the judiciary and the executive branch.

On Aug. 14, District Judge George Daniels found that families of the victims suing the head of two Saudi charities in New York could not pursue their case because the nonprofit chief, Abdul Rahman Al-Swailem, qualified for immunity.

Sen. Chuck Schumer, D-New York, responded a little more than a month later by introducing the Justice Against Sponsors of Terrorism Act (pdf) to help families of attack victims break through the Saudi's shield.

"The bottom line is that victims of terror on American soil ought to have an ability to hold accountable the foreign powers and other entities that fund the hate-filled organizations that inflict injury and death on our fellow citizens," Schumer said in a statement this past September. "Unfortunately, our courts have prevented that and allowed countries like Saudi Arabia that has provided financial support to terror-linked operations to escape any repercussions."

Weeks after the bill's introduction, Daniels pruned two more defendants from the litigation, including the kingdom itself and the Saudi High Commission for Relief of Bosnia & Herzegovina.

On the heels of Obama's trip, the New York Times reported on Friday that Saudi Arabia threatened to sell of billions in U.S. assets in retaliation if Schumer's bill passes, and that the Obama administration has lobbied against the bill to placate the kingdom.

Obama officials have also warned of broader diplomatic and economic fallout for generally allowing such lawsuits to proceed.

A lawyer for the plaintiffs did not respond to a telephone request for comment.

With New York bracing for a primary on Tuesday, both of the Democratic candidates came out in favor of Schumer's bill, though the Bernie Sanders campaign hit the issue harder and sooner than Hillary Clinton.

While both Sanders and Clinton backed the legislation, the Vermont senator went farther in calling for more sunlight to shine on the Saudi section of the commission's report.

"The families of those lost on that terrible day have the right to review any evidence that connects the hijackers to foreign supporters, including potentially those in Saudi Arabia as former Chairman Bob Graham of the Senate Select Committee on Intelligence has suggested may be the case," Sanders said in a statement.

Graham, who spent nearly two decades as a senator from Florida, has been outspoken on the issue of Saudi ties, which he used as fodder for the thriller "Keys to the Kingdom."

The Sanders campaign added: "If no such connection exists, then our country deserves the information necessary to put that speculation behind us."

Hillary Clinton's campaign did not respond to an email requesting comment on this issue.

To Learn More:

Angry 9/11 Families See Obama Capitulation to Saudi Threat Over Congressional Bill on 9/11 Lawsuits (by Mark Mazzetti, New York Times)

Convicted 9/11 Plotter Claims Members of Saudi Royal Family Helped Finance Attacks…He’s not Alone (by Steve Straehley and David Wallechinsky, AllGov)

Judge Rules Saudi Kingdom Immune from Legal Action by 9/11 Victims’ Families (by Noel Brinkerhoff, AllGov)

Why is Obama Still Hiding the 28-Page Report on Saudi Royal Family Involvement in the 9/11 Attacks? (by Noel Brinkerhoff and Steve Straehley, AllGov)

Federal Court Reinstates Saudi Arabia as Defendant in 9/11 Survivors’ Lawsuit (by Noel Brinkerhoff, AllGov)