While the world waits to see how much of Congress actually shows up Tuesday to Israeli Prime Minister Benjamin Netanyahu’s joint address on the Iranian nuclear program, support is reaching critical mass for legislation that could change the dynamics of the ongoing multilateral negotiations between Tehran and Washington and the other four permanent members of the UN Security Council.

Freshman Sen. Thom Tillis (R-N.C.) announced Monday that he is co-sponsoring a bill that would either trigger sanctions against Iran if talks collapse, or mandate intense congressional scrutiny of any deal, if the parties arrive at an agreement.

President Obama has said he would use his authority to veto the bill. But Tillis’ support brings that threat closer to irrelevance. The number of Senators who have attached their name to the legislation is now 49–a contingent that includes eight Democrats.

If all Republicans in the Senate back the measure, its original authors, Sens. Mark Kirk (R-Ill.) and Bob Menendez (D-N.J.) would almost certainly be just three Democrats shy of bringing Congress halfway to overriding a Presidential veto. Two Democrats who didn’t sponsor the bill, Sens. Jon Tester (D-Mont.) and Mark Warner (D-Va.) voted for it in committee.

The Senate needs 67 votes to neutralize a President’s refusal to sign legislation, and there are currently 54 Republicans serving in the body.

The legislation, known as Kirk-Menendez, contains additional sanctions and would require the White House, the State Department, the Treasury Department, and the Director of National Intelligence to brief Congress on any accord within five days of its completion.

Included in the language mandating the reports are clauses that would force the administration to outline hypothetical scenarios through which Iran could violate the agreement and impede compliance verification.

In addition to the possibility that these reports could give fodder to hawkish lawmakers looking to embarrass the administration through leaks, the White House has previously voiced its opposition to the bill, saying that even the threat of new sanctions, at this juncture, could undermine the US delegation’s credibility and erode the international coalition that is giving the penalties more of an effect than the United States could create unilaterally.

Recognizing the President’s concerns, Menendez, the ranking member of the Senate Foreign Relations Committee, and other Democrats who back the measure have pledged to oppose its advancement until March 24.

But the political capital spent on building support for Kirk-Menendez could easily prove fungible vis-a-vis another bill seen as a poison pill for diplomatic efforts. Senate Foreign Relations Committee Chair Bob Corker (R-Tenn.)–who noted in January that he spoke with British Prime Minister David Cameron about international opposition to additional sanctions–last week introduced a bill that would grant Congress the opportunity to have a final say on the agreement. The Friends Committee on National Legislation—a Quaker-founded anti-war group—has said the initiative would force a conflict-seeking Congress to approve of what is a temporary deal “before it’s been fully implemented”; an event that would effectively kill diplomacy. The National Iranian American Council echoed those concerns in a statement, cautioning Congress that the bill’s passage could cause the US to “fail to meet its commitments should a nuclear deal be reached.”

If a post-Netanyahu speech panic occurs, the Senate could easily rally around the Corker legislation to put the kibbosh on President Obama’s historic outreach to Tehran. Lindsey Graham (R-S.C.) had initially been described as the sole lead co-sponsor of Corker’s proposal while it was being hammered out, but Menendez’s name is now second to Corker’s, giving the legislation more of a chance of gaining override levels of support. And although the bill was introduced less than a week ago, four other Democrats besides Menendez, and Democratic caucus member Sen. Angus King (I-Maine) have all signed on as cosponsors.

President Obama said on Saturday he would veto it. But ultimately, the logic and veracity behind his and his allies’ arguments might not matter. Republicans are enthusiastically welcoming Netanyahu and his assessment of Iran’s nuclear program, despite the fact that it has proven woefully unreliable for over twenty years.

In throwing his weight behind Kirk-Menendez, Tillis reinforced the historical ignorance informing this all-out assault on diplomacy.

“The Iranian regime has repeatedly proven it cannot be trusted to simply drop its nuclear weapons ambitions, and Iranian forces and proxies have helped destroy civil society in Lebanon, Syria and Iraq,” he said in a press release issued Monday, as if Iran and its allies, such as Hizbollah, were operating in a geopolitical vacuum.

In Syria and Lebanon, there are over 1 million Palestinian refugees, prevented by Israel from returning to the homes that their parents and grandparents were expelled from since 1948. America’s despotic friends have supported a fundamentalist insurgency in the former, and Israeli forces have occupied and repeatedly attacked the latter — sometimes indiscriminately; sometimes with an enthusiasm for mass death, as the Israeli forces who in 1982 enabled the Sabra and Shatila massacres exhibited.

The war in Iraq, meanwhile, claimed the lives of hundreds of thousands of Iraqis after it was launched by President Bush in 2003–again, it was alleged, with the aims of stopping a nuclear weapons program that didn’t exist; again with the support and encouragement of Netanyahu. It was American officials who set up Shia death squads during the occupation and used weapons that doctors say are causing “catastrophic” birth defects in Fallujah.

The likelihood of similar atrocities being repeated in Iran grows if nuclear negotiations are thwarted by Congress. That drama will play out after the Israeli Prime Minister leaves town.