WASHINGTON – Two Pennsylvania Republicans are pushing a bill that could stop the international nuclear deal with Iran deal unless the country pays $43 billion it owes U.S. victims of terrorism – prompting a veto threat Wednesday from the White House.

Rep. Pat Meehan, of Delaware County, is nonetheless expecting the House to pass his proposal as soon as Thursday. His plan would bar President Obama from lifting sanctions on Iran until it pays restitution for terrorism it sponsored. Sen. Pat Toomey (R., Pa.) introduced a companion bill in the Senate.

"Why was this never a term that was included in the negotiations?" Meehan asked at a news conference Wednesday. "If this opportunity is squandered, in effect you'll have judgments that are unenforceable."

Iran will gain access to tens of billions of dollars in frozen assets (estimates range from around $29 billion to $150 billion) once sanctions are lifted as part of the nuclear agreement. Meehan said Obama should have insisted that some of that money be given to the families of terrorism victims who have won judgments in U.S. courts, but received no payments. The president "has to answer to the victims why he believes it's more important" to return money to Iranians.

As precedent, he pointed to a 2008 deal with Libya that forced that country to pay $1.5 billion to victims of the Pan Am Flight 103 bombing and a bombing of a Berlin disco as a condition of renewed relations with the U.S.

Meehan was joined by Kenneth Stethem, whose brother, Chief Petty Officer Robert Stethem, was beaten, shot and killed during the 1985 hijacking of TWA Flight 847. His body was dumped on the tarmac. A federal court awarded his family $300 million in punitive damages to be paid by Iran in 2002.

"If the president doesn't take the opportunity, and Congress doesn't take the opportunity, to hold Iran accountable for their terrorist acts now, I have to ask, when will they?" Stethem asked.

In Pennsylvania, three victims of Iranian-backed terrorism are owed more than $800 million, according to Toomey's office.

The White House said it focused its negotiations solely on Iran's nuclear program, which it said led to more international support for the deal. Blocking the agreement by stopping the promised sanctions relief "would greatly undermine" national security interests, said an Office of Management and Budget policy statement.

"It would result in the collapse of a comprehensive diplomatic arrangement that peacefully and verifiably prevents Iran from acquiring a nuclear weapon," said the OMB release. In turn, Iran's nuclear program would be less constrained, international sanctions would collapse and the agreement's disintegration would "deal a devastating blow to America's credibility."

The White House promised a veto if Meehan's bill reaches the president. That eventuality seems unlikely. Enough Democratic senators support the Iran deal to block a measure that could effectively kill the pact.

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