For critics of the Obama administration’s nuclear negotiations with Iran, it was an ace in the hole: a bipartisan bill subjecting any deal with Tehran to congressional review.

It was first the result of teamwork between Senate Foreign Relations Committee Chairman Bob Corker and ranking Democrat Bob Menendez. After Menendez’s indictment, Maryland Democratic Sen. Ben Cardin took over.

The issue united an overwhelming majority of Senate Republicans with Charles Schumer, the man most likely to succeed Harry Reid as the leader of Senate Democrats.

Now fractures are suddenly appearing in the coalition behind Corker-Cardin, with Iran hawks potentially the most split.

That’s because the latest unamended version of the bill is less ambitious in what it seeks to do. It would instead delay sanctions relief and give Congress time to review, and potentially vote, on the deal. But it doesn’t actually require congressional approval of the nuclear pact for it to go into effect.

Some Iran hawks support Corker-Cardin as the least bad of all available options. South Carolina Republican Sen. Lindsey Graham has gone so far as to say blocking the bill will only benefit the Iranians. The Wall Street Journal editorial page opined, “Until the U.S. elects a President who is serious about stopping Iran’s nuclear bid, Corker-Cardin is the best bet for censuring Mr. Obama’s misbegotten diplomacy, and giving his successor a fighting chance to reverse it.”

The American Israel Public Affairs Committee has been lobbying for the rejection of amendments that might hurt the bill’s chances or attract a presidential veto, including amendments intended to express solidarity with Israel. Bloomberg News quoted one AIPAC official as saying, “The first and foremost priority is to make sure the bill gets passed to make sure congress is guaranteed a chance to pass judgment on the deal.”

But not all skeptics of an Iran deal agree. “There is no reason to think passage of this bill, as it now stands, significantly increases the chance of reversing a deal once it is agreed to,” writes Bill Kristol in the Weekly Standard. “There is every reason to think, if the bill passes without serious debate, that it will have the opposite effect—giving the illusion that Congress is doing something to stop or slow down a bad deal when it really is not.”

Andrew McCarthy argued in National Review that “it would be a mistake to pass the Corker bill out of frustration,” contending it gives an Iran deal “the patina of legislative approval.”

“It would bolster the Security Council’s rationale for endorsing the deal,” McCarthy continued. “It would encourage other countries to drop their sanctions against Iran. It would undermine the next president’s ability to renounce the deal.”

Consequently, some Republican senators—many of them running for president—are offering amendments that could blow up Corker-Cardin unless Corker-Cardin becomes more likely to itself blow up an Iran deal.

One amendment that could obtain enough support to pass is a proposal by Marco Rubio and Tom Cotton to require Iran to recognize Israel’s right to exist. Rubio challenged the amendment’s opponents to “Come here and explain to the world” why they were voting against it.

Yet these amendments are widely seen as more likely to kill Corker-Cardin than to substantively change any Iran deal. That would likely mean that instead of weak congressional oversight, there would be no formal oversight. (Rubio supported Corker-Cardin in committee.)

This seems apt. While a diverse set of foreign-policy thinkers have expressed misgivings about the announced framework with Iran, including Jim Webb and former Secretary of State James Baker, some lawmakers appear dubious of any realistically achievable negotiated settlement of the Iranian nuclear issue.

A common criticisms of this position? Foes of Tehran talks have proposed no viable alternative for maintaining international pressure on Iran and oversight of its nuclear program.

Having gone from wanting a perfect deal to a perfect bill aimed at keeping Congress involved in the Iran nuclear agreement, hawks may be running out of options.

W. James Antle III is managing editor of the Daily Caller and author of Devouring Freedom: Can Big Government Ever Be Stopped?